Gems 101 is a puzzle where the goal is to destroy all gems on the board. Touch groups of two or more gems and they will disappear. But beware: the order in which you do this makes a difference.
You can also enter the Blitz mode and compete against time, take the Daily Challenge beating the highest score other players made, or spend some time in the lab to create your own levels, which you and other players around the globe can later fetch and play.