Collections consist of items that can be obtained in each room.  In every Bingo room, calling Bingos earns you valuable collection items. These items are  essential  for completing collection levels and unlocking rewards. With each level you advance, the rewards increase,  providing greater incentives for completion. 

To finish a room entirely, aim to complete all available levels within it. This ensures full room completion and maximizes your rewards.

 To learn about the Bingo calling mechanic, room information, and collection mechanics specific to each Bingo room, simply tap on the information icon depicted in the image below.