Open the TeamSpeak 3 app and click on 'Bookmarks'. In the lower left of the screen, tap the '+' button and you will see an empty mask:
Fill out the mask with your server data to connect to your server, so it looks like this example:
Label: TeamSpeak Public
Server Port: 9987
Click the 'Done' button in the upper right corner once you are finished. Now choose your added server from the bookmarks menu and hit 'Connect to server'.
This is also explained in our video tutorial here http://www.teamspeak.com/?page=tutorials&type=client#ts3_tutorial_4