Contests are one of the ways to show that you’re the ultimate Gin Rummy player! You can find out which Contest is happening when it ends and how much the total pool is using the banner that appears over the corresponding tables. 

You can also click on the Contest tab on the bottom left side of the screen:

 and find all the information about the contest including the current rankings and prizes.

For example:

You can find more information by clicking the blue 'i' button at the top corner: