Before downloading anything Launch Vanilla Assetto Corsa (for anyone who didn't play already) this is due to the game needing to download
Microsoft .NET
Scripts
other stuff
once you've done this proceed to Step 2

Look mods for this game without this piece of masterpiece of coding is like putting a big mac into a dog pit absolute chaos so some hunky guys made the Assetto Corsa Content manager
how do i download? simple
go to https://assettocorsa.club/content-manager.html
then scroll to the bottom of the page you will find a free version (which i use myself) then download it
when opened they will ask for the root folder of the game
the Root Folder will look like c:/programs86x/steam/steamapps/common/assettocorsa
(please note i spelt that wrong so its a non replica of it)
once done you should be in
Proceed to step 3!

So now for the entertaining part, downloading the Mods
so CSP (Custom Shaders Pack) May appear in some car mods heres how to download CSP!
go to settings in content manager,then go to Custom shaders pack here press install
now once you have your track or car drag the ZIP file into the content manager and press the download button on the top Right once pressed press install then wait,once done thats it!
Well done Youve modded your Assetto corsa
(Yippe)