If you're planning on releasing a "cs:go" mod on this website - by this point it'd just be a pointless duplicate of what has already been released on here.
If you're doing this for personal use - there's plenty of stuff available on here. Sadly, nobody's willing to literally recreate every texture from CS:GO for use in CS:S and what not.
Now, how to do such a thing: Utilize many programs, take time learning how to port materials, models, properly format scripts, and sounds. Personally, I recommend this way of doing such a thing, as it would become faster over time, instead of just 'taking' someone else's work. (Not assuming you do that) I'd also seek out tutorials online - I don't know any personally since I've learned mostly by myself in the past 2-3 years.