As you play games and daub the correct numbers, you gain Experience Points (XP). Every time you daub a number on your card that has been called out, you gain XP equal to the ticket cost of 1 card depending on a room you play in. For example, if you play in the Farm room, you will gain 1 XP per each correct number that you daub.
When you gain enough experience, you will receive a level up. All players start at level 1 and work their way up through levels. Each subsequent level will require more and more XP to unlock, however, new levels unlock new rooms. If you play in higher level rooms you will level up faster!
Your Current Level
Your current level is displayed in the top left corner of your game, under the player name. If you click on your name, you will see how many XP do you have and how many do you need to reach the next level.