Whenever Valve adds a new update to "Team Fortress 2," they always present the announcement in a humorous manner. The addition of the Mann Co. in-game store is no different, and you can enjoy their amusing gorilla sweepstakes and legless drawings here. But, if you're hoping to understand what this new store is really all about, that page is probably not terribly helpful. I'll do my best to straighten it out for you.
At a basic level, the addition of a store allows players to purchase in-game items for real money. Before the store, players would have to rely on crafting and "drops" to score a certain item or weapon. This leads to tedium and frustration for some, and the store is a way of alleviating that.
Right now you can hop in the store and buy new weapons, armor and yes, hats, for real dollars. People crying foul, saying that they've already payed for the game, should note that all of the items in the store can also be found through traditional drops or crafting. Using real money is basically just a shortcut for instant gratification.
But the store isn't just for paying customers. Players will be able to trade and gift crafted or found items to other players. Purchased items can't be traded, but anything found outside of the store can be given and used by anyone.
The store has 65 new items for purchase, including 5 new item sets for the Soldier, Scout, Pyro, Sniper and Spy which were created by community members. Those community members who created the items will actually get a portion of the proceeds earned from the in-game store.
I'm sure the addition of a for-pay store to "Team Fortress 2" will be divisive, but considering the game continues to offer up all of its content for no additional cost post-release (presuming you are willing to work for it), I think there's nothing wrong with letting people spend money instead of time to get what they want.