@buff_mac466 depend what you want to do there is a lot of different kind of mod ( map, vehicle, script, retexturing, skin, weapons etc etc).
I invit you to visit tutorial topic of the forum that contain some intersting stuff to learn.
also for moddeling, there is tutorial over youtube mostly for vehicle ( on Zmodeler) but not only
https://forums.gta5-mods.com/category/8/tutorials