Everything is very intuitive, just act like you are on a real ATM machine. Click "Start" to start. Then you can click on any of the two debit cards to insert it into the ATM machine. A menu will be shown once a card is inserted. Choose any of them. They are very self-explanatory. The "Exit" option can let the ATM give the card back to you, thus you can insert another card. At anytime, you can click on "Leave ATM" to leave the game, but if you attempt to leave the game with a card inserted in the ATM, you are not allowed and will get a big warning! :)
thank you qixi for atm simulator