are there any step-by-steps on UV mapping
If you’re talking about how to create UVs for a mesh, this is a pretty large subject and no single tutorial will tell you everything you need to know.
In Zbrush there are a number of ways to create UVs. For complex texturing, the most popular way is probably using UV Master. Start with the UV Master documentation–it contains information you need to know, and also has a few basic tutorials.
After that I think you’ll be able to find quite a few tutorials from people working with UV master. Be sure to check out the UV Master videos in the Pixologic Classroom.
Good luck!