DO NOT LISTEN TO THESE NON-INFORMED MEMBERS!
The problem is that you have restrictions enabled. To fix your problem do the following :
1) Tap Settings.
2) Once in Settings; > General > Restrictions
3) It will ask for a passcode, at this point, if you have no clue then its time to interogate your brothers/people who used it.
4) Once you have the passcode, disable all restrictions.
The list of restrictions show as posted in this quote :
You can choose to restrict access to the following applications and features on the device:
- Safari
- YouTube
- Camera (also disables FaceTime)
- FaceTime
- iTunes
- Ping
- Installing apps
- Deleting apps
- Multiplayer games in Game Center
- Adding friends in Game Center
Source