In order to start playing, select “New game” located at the bottom of the screen. You’ll now be able to choose an opponent that will either belong to your Friends List (if you logged in via Facebook), or a random opponent if you choose “Random”. Moreover, you’ll have the option of inviting friends via different means by pressing the button “Invite”.
After choosing your opponent, press “Play” to start the game. On your very first game, you’ll be able to read a short tutorial that will explain you how to play, as well as provide you with information about the rounds and the multiplication bonuses.