You're right, there's a lot to get your head around with CM.
I recommend you do a system image of your C drive after doing a clean install of AC and CM. That way you can always roll back your PC to a clean state if you feel things are too messed up. You should also take a copy of the entire AC game folder under ….\common\ in case you want to restore default file set, cars, tracks etc.
If your PC is reasonable then you should install the latest Custom Shaders Patch and latest SOL mod. You can install latest
Once you have both of them you can tweak additional video effects in the Custom Shaders Patch tab and you can select the SOL_ACC post process filter from the Assetto Corsa Video tab.
Now when you are in game you can open the SOL Config app and play with time of day, weather etc. It can take a while to get to grips with all the light settings to get how you want. I had a lot of trouble with headlights not working and found using a gamepad was causing a lot of the issues. When I used a wheel it all seemed to work easier for the headlights. I remember having to tick the box for 'turn on headlight lights with AI' for them to work. Don't ask me where this setting is as I always forget (not in an obvious location). You need to play with this setting to see what works for you. Don't forget to map headlights on / off to a wheel button as well.
Remember to save CM settings as new profiles so you can always go back to known good settings. Different tabs have their own profiles you can save.
Car and track mod zip files just have to be dragged from explorer to the CM window. You will get a little green icon appear in top right of CM, click on this and select install mod that is now listed. This usually works for cars / tracks / skins / sounds. You sometimes have to be careful that the zip file has the right folder structure to align with what you have installed (most issues when installing skins and sounds as they don't always point to the right car or track folder.
If it all becomes a mess then you will still be able to roll back with the backups I suggested.