2
What are you trying to do?
To add a theme, you just copy it to the /themes directory, which you already did.
To change the theme permanently for all, you just select the theme that you want to use in Admin -> Preferences -> General Settings
To easiest way to change themes for individual users is to activate the "Themes" block and make it visible to Admin (or to any group that you want to allow to change themes), and change it there.
For general info about XOOPS management I recommend the
XOOPS Operations GuideFor theme development/modifications, there is no better book than the "
Design for XOOPS" book