Aim of the game depends on the difficulty you selected but all difficulties have the same rules being basicly you select a peg, it will turn blue then select an empty spot. Between the empty spot and the peg you selected should be another peg so that the initally selected peg will jump over the “middle” peg and will be removed.
Depending on the difficulty you either have to end in the middle of the board with one peg left or on any location (also with one peg left). And you can “jump over pegs” diagonally, but that’s explained ingame as well on the difficulty select screen.
To start playing copy the rubido.app file to your game3d folder and launch it. It will take around 5-6 seconds to load it.