Bingo Pop Rooms on the main path are unlocked by reaching a certain player level - you can see the level you'll need to reach on each "locked" Room icon.

 

Your current level is the number beneath your profile picture in the top left of the Bingo Lobby. Increase your player level by earning XP (Experience Points)! 

 

Your current XP progress until the next level is tracked from the border of your profile picture. The border will start to fill with a green colour when earning XP. Once the border has been completely filled, you will advance to the next level.