Those free games are earned by completing a series of in-game objectives which cycle everyday until January 1. Completing them either gets you a freebie off the "Great Gift Pile" or a lump of coal, seven of which can also be traded in for an actual gift. Alternatively, you could save your lumps up -- each counts as an entry into a Steam sweepstakes, the grand prize for which is every game on Steam ever. Seriously, that's not hyperbole. The prize is every game.