Tap the button above the Play button in the Lobby to choose a game mode. Select a game mode, then tap Confirm to apply your choice. Choosing a game mode will take you back to the main menu, where you can tap Play to start your match.

Within the game mode selection menu, you can also use the tabs at the bottom of the screen to choose between Public and Private matches.

Be sure to check out the Help section (open the menu in the Lobby and select Help) to access more gameplay details.