You'll note that all functions begin with the letters Zip. To avoid conflicts with RxZip function names, do not name any of the functions in your REXX script starting with those 3 letters (neither upper nor lower case). Also, do not use the variables ZipErr and ZipHeading for purposes other than setting error handling features.
The sections of this book leading up to the list of functions describe how to do various tasks with the RxZip functions. So, they are overviews (ie, tutorials) of how to use RxZip in various ways, whereas the list of functions are more of a reference complete with incidental notes/details.