There are two methods to install mods on Project Zomboid. The first method is to go through the Steam Workshop, which you can find in the Steam Library menu for the game, or you can use the Nexus hub and the Vortex app to download and install mods. I would recommend using the Steam Workshop mods, as there are many more available on this platform. Also, as your game is running on Steam for the most part, it is very unlikely that there will be any silly errors occurring in some background files you will have to spend hours searching for. All-in-all, the Workshop experience is simply much smoother.