L = light attack
M = medium attack
H = heavy attack
S = special (ki blast)
SD = super dash
DR = dragon rush (universal basic throw)

1,2,3,4,5,6,7,8,9 = input directions
Look at the numpad on your keyboard, the numbers match their position on the numpad.
Ex :
4 = left,
6 = right,
2 = down,
1 = down left, etc

So 2H means down heavy attack,
5M or just M means neutral medium attack
jc = jump cancel, when you jump in the air during a combo after getting the opponent airborne.

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Not used in this guide but you might also see :
236 or QCF = quarter circle forward
214 or QCB = quarter circle back

I answered this to a reddit user, and I thought later it could be useful for others players here :

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Ok, the game is fairly easy to handle, but after almost 1 year casually playing, I can still discover new depths in his gameplay. I'll try to overview some of the basic mechanics that helped me improve soon after I started the game :

- Superdash(SD) can be done just by mashing Heavy(H) when inside a combo, much more practical than using the dedicated button everytime. Outside combos, superdashes can be hardcounter with down heavy (2H), so avoid too repetitive/obvious superdashes for opening. 2H is good against SD because of invulnerabilty's frames but it only works on ground. If your target is in the air, superdash becomes a much better option.

- Jump cancel. Train an improved version of the autocombo including cancel jump : "L,L,L =>(SD) L,L,2H,jc.L,L,L"
The timing could be tricky at start, but soon you'll do it without even thinking. You can only jump cancel once per combo before you hit the ground again, as you can only superdash once.

The universal BnB using all these features is the same on 90% of the cast :
"2M,M,jc.L,L,2H=>(SD) L,L,2H,jc.L,L,L ==> Super"
Because you hit 2H followed by SD, you are high up in the air when throwing the opponent down. That will trigger a "sliding knockdown" allowing you to connect for free with almost all supers of the game. Good start to improve your offense and average combo damage.
Note : If you look closely, L,L,L in the air will actually do the same moves as L,M,H.There's a slight difference, but for now, don't ask question and just use the simple version. ;)

- Vanish :
It should be used the most to extend combos. The easiest way is to vanish into Z-Change (L1/L2), you can then end up with autocombo (L,L,L) and then super.
But to extend a combo without switching, you'll have to learn how to catch the opponent after he bounces onto the wall. Use training to get used to the right way to do this.
Just spam some ki blast, Kamehameha, or a Heavy attack then vanish and try to catch the dummy before it hits the ground. Most of the time you have to just press forward and hit down medium(2M) after the vanish, but sometimes you may also use autocombo or stand medium(5M) to do so.
Adapting to height and distance, you may have to dash forward, or even jump+dash if you are higher in the air, in order to catch your opponent. There's a lot of way to do this, but it never changes if you vanish in the same condition, so once again, you'll soon get used to it.
You can only vanish once per combo, but it's a great way to add consistent damage output to it. Keep in mind, once you get used to this mechanic, you can convert any hit (even a single ki blast) into a combo. This will really give you the edge if you can and your opponent can't.

- Assists :
I spent waaay too much time before I really started to use these. Trust me, it was a huge mistake. This is a 3v3 Tag battle, and assist as Z-change are core of the game.
Find a character with an assist you are very comfortable with. For me it was Goku SSJ's one, but Vegeta assist is very strong too. They all have different speed, duration and range, just find one you feel good with. Then learn to use it, and even abuse it. Assist are almost no risk and if it connects, you can often superdash into it for a free combo. You start with two of them, and the cooldown is not so long. Plus it will reset if you kill one enemy.

So remember, it's always better using assists too much, than "keeping it for later". Later you'll learn to reserve assist to extend your combos even more, but for now, just get free combos. One exception, don't call assists to save your *** if you feel it might be too late, you might just end up with both your characters caught in a combo, and that's not what you want.

Last thing about team comp, your best assist will probably be in third place, so you can use it longer. In contrary, the character that benefits or needs the most of assists should be first in your team, so you can have 2 assists available for it before anyone gets KO.

- Defense :
This is not always true, but trust me, learn this as a rule of thumb for defense : When the opponent is on the ground, block low. When he's on the air, block up.
When you want to tech a dragon rush (R1, basic dbfz throw) use dedicated button, not L or M alone, they can work but are not reliable for this. Be careful when you want to switch a low life character, it's risky and will become more and more predictable as much as you climb the ladder. Prefer to switch safely after a vanish during a combo, or after a a lvl1 super at the end of it.
True combo's numbers are orange. If the enemy's combo numbers are blue it means you miss an opportunity to recover. So when you are getting struck by a combo, keep pushed the light button, it will allow you to recover 100% if possible. Input one of 4 directions will change the direction of your recovery. Down recovery is the fastest and often the best choice, also you can use recovery direction to get out of a corner pressure.
Very important thing, unlike many others versus game, in dbfz jumps are punishable. It means when you jump, there are frames where your guard isn't up. You'll see a lot of people trying to catch you with ki blast or beams when you just wake up at the other side of the screen and think you are safe to jump. You can of course do the same.

- Reflect : Reflecting (4S) is rarely about reflexes, but more often reading your opponent's next move. If you are in a situation you want to mash light, but you are not sure you'll get priority, that's probably a good time to reflect. Same thing if you feel overwhelmed by too many hits.
But be careful, if your reflect is predicted, it's 100% punishable.
If you see your opponent using reflect too much, try dragon rush, it's natural counter.
Learn to counterattack without hesitating just after you input reflect, don't wait to see if it works.
2M is often a good choice, but a lot of special moves are great too. Most of the time, one reflect is enough, but some character's moves and autocombo will need two or even three reflects before you can safely counterattack.

- Blockstrings : Ok, this is going to be a little bit more advanced mechanic, since at the beginning, no one is really playing defensively. But soon, your opponents will, and then, you'll need blockstrings to help you break their defense.
Blockstrings are kinda of a combo, but you'll do it on the opponent guard until it breaks. So it's more a "pressure combo" in order to get a real combo going.
The universal blockstring for most of the character is : "L,L,M,M,H + special move."

After this first blockstring, you have option to vanish, and spam L to start the blockstring one more time. A well timed assist will have the same effect. This is very important you learn to use your assists this way, because it will force the opponent to keep blocking the moment you are supposed to be open for his counterattack.
This way, using your 2 assists and a vanish one after the other, you can repeat 4 times a same blockstring which will be nearly 20 sec of pressure on your opponent :
(1st blockstring, A1, 2nd blockstring, A2, 3rd blockstring, Vanish, 4th blockstring)
And of course the fun will start when you'll learn to introduce differents variations inside of your blockstrings to create a real mindgame in your offensive pressure.

Don't abuse pressure extend's vanishes though because they can be punished. By using reflect (4S) + or spamming lvl3 just after the vanish. Btw, a perfect blockstring is when there's no gap to reflect or escape within the pressure.

When you start to dig this way, I can only recommend you the "What to do on block series" on YT. There's one for each character of the game, and it will show you how to break defense with your favorite one, and how to defend against your nemesis. It's not for the first weeks of playing, but I put it here because it was a huge step up for me, especially in improving my defense.

- Training mode : It's a lot more useful than you could think at first, I will let you dig later, watching tutorials when you need it, but just to inform you that the training mode brings a lot of handy features that could help you to train in a smartest way than just doing combos and blockstrings again and again.
For example, setting the dummy on a specific counterattack can help you check if your pressure is safe. Using random guard dummy can help you to react naturally and convert an opening, anywhere in the pressure, into a real combo.

When you will be confortable with all this, try to look for "neutral game tutorials".
But, when you get there, you won't be a beginner anymore. ;)

- Last advice : Enjoy the game, embrace victory, accept defeat. Unless you aim to become the new SonicFox or GO1, there always will be better than you on the servers, plus the matchmaking algorithm will try to balance your winrate to 50%. So definitely, you won't win every game. A good game is a game you did your best. Fairplay and respect is a good way to accept defeat.

It feels always better to be beaten by someone you respect and admire than someone you despise...

Hope I helped you and all these newcomers to this wonderful game ! ;)