The BET ONE button allows you to increase the number of coin being bet one at a time. When the maximum number of coins is reached, the count re-starts from one. You will have click on the SPIN button to spin the reels.
The BET MAX button allows you bet the maximum number coins allowed by the game, and starts the reels spinning. The BET MAX button allows you to win on all pay-lines available for that game.
The SPIN button allows you to start the game.
The STOP SPIN button allows you to stop the spinning reels.