You have to match tiles in pairs until all of tiles are gone.
Once two tiles have been matched, they will disappear from the board.
When you click on a tile - it becomes highlighted.
In order to select a tile, it must have at least one side edge free.
(no other tiles touching it, and cannot have any tiles on top of it).
A context menu should be shown when right-clicking or, on touch devices, long-pressing in the game. This menu especially allows to play in full screen and control the volume.