Freeroll is poker tournament that is free to enter. It is a way for poker rooms to promote poker and give an opportunity to test your skills for free. Although regular freerolls do not have much value, there are always different promotions going on and you sometimes might find a really good value freerolls (up to €100 entry). Anyway freerolls are fun and opportunity to play real poker without risk.
When you play a freeroll you should consider that most players there are either havent got a clue about the game or dont care that much about the tournament. As a conclusion your bets wont be respected and it will be hard to guess your opponents cards. Therefore you should play simple and straightforward poker: play only good starting hands, make bigger bets and raises, attack with good combinations and never bluff.
In the early stage of the freeroll, its common for players to go all in right away. Good advice would be to wait for AA, KK, QQ or AK and just push them all in. In late positions you can also raise JJ, TT and AQ. Never limp (call the big blind) just to see the flop as you will end up loosing your blind when someone raises.
Later in the tournament when you will have between 15-25 big blinds left, most of the maniacs who go all in all the time will be gone. If you are holding hands like AA, KK, QQ, JJ, TT, 99, AK or AQ, you should raise to four big blinds. From late positions you can also consider raising KQ and AJ but if someone raises you all in, you will have to fold these 2 hands.
When you have less than 10-15 big blinds left, you should start raising all in again as the stack is really small and there is no point in seeing the flop. Raise only good cards from early positions and respect the raises from these positions, so you should play only AA, KK, QQ, JJ and AK in these situations. In middle positions it is fine to raise or to call the raise from these positions with AQ and TT. If you are in late positions and these were no raise, then you can push with 77+ and KQ.