BitCoins are an online currency that are worth around $100/per 1 bitcoin, you can get very small amounts like 0.000025(like 2.5 cents) and such. You need the bitcoin program thing that will have a special code that people will send bitcoins too. You make bitcoins by getting a bitcoin miner, but it's better to trade things for them, like items in TF2 or something since you would have to leave your computer on for around 6 years to make 1 bitcoin. The power costs aren't very good.
They are highly unstable. It would be so OP if you could convert them back to US dollars or something.