what are tf2 keys exactly?

yep your right

They're magical keys, when obtained they transform into a pokemon.

Just kidding, Yes, they are Mann Co. Supply crate keys.

Thanks guys, i'm not as confused anymore :3

Where this key coming from? Do you need to craft it?

does anyone actually using them for opening crates? i thought they were a stable currency in gabe's wonderland.

They're keys which are supposed to be used for opening crates. Of course, you have to pay real life money for them, and most of the items you uncrate are relatively worthless, unless you're super lucky and you unbox an unusual, which is a hat with some cool particle effect on it.

Keys are pretty much used as currency now, and nobody actually unboxes because the price of keys relative to TF2 items keeps increasing.

A way to launder money from stolen credit cards and so on. The reason I never trade using this stuff.

They're items from the cash-store of a game called Team Fortress 2.
In-game, you will gain random items at semi-random intervals, and one of them is a locked crate. To open it, you need to purchase (or trade for) a key.

People use these keys as a bartering currency.