I can link you tutorials, the same tutorials I've used when I first started
this video here teaches you from modelling, texturing and compiling using the import (the import is for cosmetics only)
www.youtube.com/watch?v=zCMt-j…but since you're making a weapon, watch this old version of the tutorial because it shows how to manually compile items (weps and cosmetic)
www.youtube.com/watch?v=-X5QGx…but if you're going to follow that second tutorial after learning how to decompile models using mdl decompiler, write qc files and compile them with gui studio mdl, instead, use crowbar for compiling and decompiling
steamcommunity.com/groups/Crow…