perl comes with it's own documentation tool, perldoc, although it's usual for regular manual pages to be generated and installed as well.
perldoc can be used to search for perl-specific documentation on your system. For example, to see the docs for HTML::Parser, you can just enter
You can also search for specific perl built-in functions, like this:
Or you can search for keywords from the perl FAQ like this:
If all that fails, look at the .pm module files themselves or .pod files in the same directory as the .pm files - they may contain pod tags which you can turn into a nice readable form using perldoc on the file, like this: