When you start a "FarmVille 2" game you are given 100 free Farm Bucks. There is no other way to get free Farm Bucks past this initial gift.
You can use these Farm Bucks to make fast progress in the game or buy goods. To acquire Farm Bucks you will need to pay with a credit card, PayPal, bitcoins, mobile, a game card or with your Facebook credits. As of May 2015, you can purchase 1,010 Farm Bucks for $150 through Facebook or through the Zynga website directly. The Farm Bucks will instantly be added to your account so you can use them right away.