its a nice feature in IOS 6 , called application or certain area lock or how the apple called it guided access .
this is very useful if you want to give your mobile to a person and want her/him to check certain thing not to play or moving to other things .
even if you want to share one photo with a person not letting him to browse other photos keeping your privacy safe .
how to enable it , simple
go to General
under learning tag , choose guided access
enable it and set your own 4 digit password
after that to utilize this feature
you need to open any application you want , then push the home button 3 times .. a menu will appear . you can click start button and it will work . to exist this 3 times push home to unlock
for picture or specific area only . then circle the place you want and click start.