To use PVM, they must set PVM_ROOT (§2.8). They should also set MANPATH (§2.20) if it's supported, to be able to read on-line manual pages.
The easiest way to get started is to copy the examples from $PVM_ROOT/examples to $HOME/pvm3/examples, compile them and try them out, modify them, etc. There are small tutorials in the PVM book and user guide.