In reality: Put in an amount you are willing to lose. You're more likely to lose it all (or much of it) before you decide to move on. It depends on what kind of player you are. I know many people that just play for fun, and are perfectly happy just dropping in aR$20 and playing a machine until it's gone.
Choose the slot machine you wish to play. Put the money in the bill acceptor. Money inserted will be shown in the 'Bank'. Collect your winnings by pressing the cash out button.