From what I can remember of the PC version of this game, this works in pretty much the same way.
It's very addictive. I find myself shutting the game down only wanting to start it up again right away!
You can play in two ways - free-form or tutorial/scenario.
The freeform game lets you do what you want with your Zoo, choosing your own basic land (the smaller the land, the easier the game play) and you can choose the difficulty level (the more difficult you choose, the less money you start out with). You start out with being able to buy a few different animals and objects. The more time goes on and the more popular your Zoo becomes, the more animals/objects you can buy.
The tutorial game play basically lets you get the hang of the game for example, how to make animals happy, setting you up for playing the free-form version.
Overall, a very enjoyable, easy to play (and addictive!) game.