I tried installing Fabric API, I put the Java file into my mods folder but it doesn't work. If i am doing it wrong please give me a step by step process on how to set it up.

You seem to be on a forge environment, and fabric's api is not supported on forge. Change your launcher profile to the one fabric created and things should work.

You seem to be on a forge environment, and fabric's api is not supported on forge. Change your launcher profile to the one fabric created and things should work.

So how do I do that? I tried opening it and it wasn't doing anything... I go to installations and its also not showing up there.

If you look at the launcher page you should see a bar down below where on my launcher it says fabric-loader-x.xx.x https://i.imgur.com/Tu3yFnN.png if you click the bar there should be multiple options on the popup. If fabric doesn't show there then install it from here:
https://fabricmc.net/use/