Ucupaint is Blender addon to manage texture layers for Eevee and Cycles renderer.
You need at least Blender 2.79 to use this addon, but more advance features are only available on the modern version of Blender (2.80+).
Go to release page and download according to your Blender version. Open Blender, go to Edit > User Preferences, select add-ons tabs and press install button, browse your downloaded addon zip file and click install add-on.
Blender 2.79: View 3D > Tool Shelf > Ucupaint
Blender 2.80 or greater: View 3D > Sidebar > Ucupaint
Please read the wiki to see the documentation and demo. It's not 100% complete, but it still can help you get started.
To contribute to wiki, you can go to the wiki repo.
You can join Ucupaint Discord to ask or discuss things related to Ucupaint