Along with the many good CGI links in the Tutorials section, I recommend picking up a copy of CGI Programming with Perl. I just picked up a copy, and though I'm only through chapter 4, I'd say it was money well spent already :-) Personally, I prefer paper media over electronic for study... For me it's just more comfortable.
As for your question, (as was pointed out above)...
GET is the standard method for retrieving a doc via HTTP. GET requests are intended to only retrieve resources and should not have side effects.
POST is used with HTML forms to submit information that may alter data stored on the server.
The above is highly condensed from chapter 2 of the above book.
Whip me, Beat me, Make me use Y-ModemG.
in reply to Get vs. POST in CGI.pm