Basically you can learn alot more about Brasil on another "forum" Im not going to pomote here.
But yes, learn Portuguese! Or at least be very good with your spanish.
"Freebies" abound, but you need to be able to talk to them. If your in Rio alot of the women you see at Help! are from the local "hoods" (ie

oor) and yes some are looking for a "hand-out" in return their companionship, at least at first...
It is NOT uncomon to find a "girlfriend" for your entire trip and it cost you less than it does to take a typical American girl out on a single date.
Be aware that some might view you as an ATM machine...
Without getting into futher detail, prosutition is accepted behavior. You don't have to go home alone if you don't want too and your vaction doesn't have to "sex-less" just because you don't know enough Portuguese or have no game to hook up with a local cutie.
You have options...
Another point I should make -
You will not have a problem hooking up with Brasilans of African decent, DUH. But if you favor more European looking ladies, then Im not saying your out of luck, but I have been told by several for free away (and its NEVER TRUELY FREE REMEMBER THAT!) its a bit harder to come by.
Depending on your budget and what you expect out of your trip, I would suggest Rio as your first place to visit if your a complete "newbie" and you will not be disapointed.