It's all based on collecting cards. There are bronze, silver, and gold cards. You start off with a 'starter pack' of mostly poor rated players (probably CHL and bad Euro league players). As you play games you get coins. You can spend the coins on bronze, silver, or gold 'packs' which include cards to upgrade your team. There's also a marketplace where you can buy or sell cards in auctions.
There will be a lot of gold cards, but the super super stars will be very rare. Ovechkin and Crosby will be extremely expensive, and you'd be very very lucky to get them in a pack.
That's the jist of it. There's some other details, like chemistry and contracts. It's pretty fun. I've gotten the past 2 versions of the FIFA one.