The game starts with a 9×9 board with three gems chosen out of seven different colours. The player can move one gem per turn, and the player may only move a gem to a particular place if there is a path (linked set of vertical and horizontal empty cells) between the current position of the gem and the desired destination. The goal is to remove gems by forming lines (horizontal, vertical or diagonal) of at least five gems of the same colour (four in the early levels). If the player does manage to form a line of at least four/five gems of the same colour, the gems in those lines are removed, and he gains one turn, i.e. he can move another gem. If not, three new gems are added, and the game continues until the board is full.
Gems are moved by selecting a gem and dragging it to an empty square on the board. Alternatively, you can tap to select a gem and then tap on the target board square. Tap again on a selected gem to unselect.
There is an 'undo' button if you make a bad move and should you wish, you can even undo all the way back to the start of the game!