PVM is a message passing library for distributed programming. As such, PVM is a predecessor to Message Passing Interface (MPI). MPI has now become the de facto standard. There is a textbook I can recommend to learn about how to design programs using message passing and parallel processing, for any language and any library because it is similar for all of them. This book will help you get the fundamentals in place to understand the big picture correctly. Studying the syntax of PVM is not going to help you at this stage. This is the best textbook for self-learners. It is written by the best teacher in the field of parallel programming.
Foundations of Multithreaded, Parallel, and Distributed Programming
by Gregory Andrews