What does 'run' do in cperl-mode?

[formido]

So, I've got:

print "Hello World\n";

... in the buffer and it's saved. I can use the debugger command to
run it. Strangely to me, 'run' is disabled. What does 'run' do? In
other IDEs I've used, I type some code, then I either compile or don't
depending on the language, and then I run. What's different here?

More generally, when confronted by a menu command, how can I easily go
to its definition?