hl2
hl2 episode 1 and 2
source sdk
source sdk 2006
source sdk 2007
source sdk 2013
half life sdk
steamworks sdk redist
source sdk base 2013 singleplayer
source sdk base 2013 multiplayer

you can use MOD DB to install mods but there are other sites for it to install

to find MOD DB just search it up on google

SO HERE IS HOW YOU INSTALL IT

1. find the mod you like and click on it

2. Click files

3. Click the newest version

4. Click the red download button

5. wait for it to download

6. when its done downloading copy paste the file you installed

7. go to your steam libary and click hl2

8. Right click on hl2 and click proparties

9. Click intalled filles and then click browse

10. go to steamapps in your files

11. go to sourcemods (its a file in steamapps file)

12. paste the mod files you installed

13. right click the files you pasted and click "extract here"

when you are done with all the stuff said in the last part you need to restart steam

after you are done reseting steam you will find the mod in your steam libary
just search up the mods name in the steam libary search bar to find it easier

if you have any problems just tell me in the comments and I will try to help
maybe I will even update this guide for the other people having this problem