They call it Visa on Arrival (VOA) but its just the same entry and exit stamps you get for countries that we don't require visa for. You don't have to do anything extra or pay a fee.

Unlike examples of Australia which requires you to pay $20 to get ETA before departure from the US or Indonesia where you have to go stand in another line first to pay the fee and get a VOA sticker before you line up for passport control.