Zynga's Business Model:

Zynga has a free-to-play business model, this means the consumers do not pay any money. So they use 2 different methods to make their money:
One way is micro-transaction. This means that players can purchase extra in-game items ahead of time, instead of playing the game for longer to earn them. For example:  You can play 50 rounds on draw something to earn 150 coins (at maximum), or you can buy 200 coins for 69p in about 20 seconds.
Zynga also sells advertising sponsorships within some games such as movie tie-ins and other brands.They will get a percentage of revenue broought in from the advertisements, a small percentage also goes to facebook.