Each branch contains the a different lab.
master contains the base for most labs. The other branches are solutions. Note that AdvancedEncryption lab starts with the BasicEncryptionSolution branch as a base.
To use the app, switch to the branch you want, run XCode in the directory and build/run on the iPhone simulator.
You will need to be running the server for this to work, information on how to run it is available in it's README.
Please see http://securitycompass.github.com/iPhoneLabs for lab descriptions and walkthroughs.