It is a setting that came available in iOS6 that I think several people overlook. So you say how do I do this...
- Learning (scroll almost to the bottom)
- Guided Access turn - on
- Set Passcode - enter 4 digit passcode twice
- Start using guided access by triple clicking the home button
- Selecting any area you want marked out or not allowed, in the picture below on the left you see I blocked off the help, store, more, and stats.
- To get our of the app triple click home, enter passcode, click resume.