If you really want free BTC, you should go for faucets. There are several of them. Just search on google for 'BTC faucet' or 'bitcoin faucet'.
There is also the option of gambling, but in order to do that, you first need to buy BTC.
Faucets pay so very very little. You can in most cases hope for a few cent's a hour. It is sad, but it's true.
I suggest finding a signature campaign and joining it. It will pay better then facet and also you would be posting anyways so win/win. Just don't spam is the biggest thing.
It's is very hard to not spam if you aren't knowledgeable about something. Since this is a Bitcoin forum, newbies probably won't have much knowledge hence, not a good choice. One or two spam posts with signature campaign can easily result in a ban. The best bet is to offer service at the service section.
Gambling? Don't try. It is very risky. Once you start you probably can't stop. Eg. Just look at my address. But still, it was fun to gamble what I could afford to lose.