The easiest way to get started with Pressbooks is to follow their 5 Steps to Getting Started on Pressbooks. You can also review the complete Guide to Using Pressbooks or brows the Pressbooks Directory to find examples of the kinds of books you can create or adapt in Pressbooks.
There is also a free User Training Video (1 hour) available on YouTube to learn the basic features of the Pressbooks platform.
You might also want to take a look at the BC Campus Pressbooks Guide for ideas on creating quality open textbooks in Pressbooks
If you need further assistance, please contact firstname.lastname@example.org.