Re-skinning Workshop models?

Good Morning/Afternoon/Evening everyone, I was wondering if there was an In-Depth guide to re-skinning models found on the Workshop for Garry’s Mod.
I’ve looked all over the Facepunch forums and couldn’t find a Guide to Re-skinning/Adding Skins to Models anywhere. i would greatly appreciate if someone could help me in this endeavor by perhaps walking me through the Steps and/or linking me to an Existing tutorial.