Learning Perl and Perl in a Nutshell both have small sections to get you started, but they're pretty similar to the perldebug manpage.

To get started in the debugger, 'n' executes the next command, skipping over subroutines. Note that the command printed in the debugger is the one thats about to get executued. 's' works like 'n' except it descends into subroutines.

'c' continues exectution until the program breaks or you get to a breakpoint; 'b line' sets a breakpoint, 'D' clears all your breakpoints.

Remember that you can also type in normal Perl statements and they will get executed.

Hopefully that will get you started and you can go back to the manpage for more info...