Select Rob Malibu to open the Beach Battles interface, where you can start a union battle or a random battle. You can also proceed to ratings and the Sandy Store to see its assortment of weapons.
To start the fight, you need to have enough water. The quantity of water is displayed at the top of the screen in the Beach Battles interface. You can replenish your supply by pressing the plus sign next to the snow bar or by waiting a while for it to restore automatically.
If you have enough water, press the button under the "Random Battle" section. It may take a while to find other players for the team. When all the players are found, the battle will start automatically.
To take part in Beach Battles, talk with a tourist named Rob Malibu. When the tournament starts, he usually strolls along the beach.