You are playing against Android, which is holding the bank. At the beginning of each part you will get one card and then you have to bet something on. Android bets the same. After that you continue taking cards from the package until you get the sum 21 or at least similar. If you get a seven as a first card you can exchange it till you start betting. Once you finish taking cards by clicking the Enough button, Android starts playing.
The highest figure are 2 aces and then 21. The winner has to gets the highest figure or has to gets the sum closest to 21, while not exceeding 21 is being preferred. In case of indecisive score the bank is taking the whole bet.