I assume you're asking why apps aren't automatically updating in the App Store. First check automatic updates are turned on. Go to Settings - iTunes & App Store and turn on Updates next to the App Store icon.
I'm not sure what stops them updating but occasionally I've had the same issue. Refreshing the App Store app sometimes kick-starts updates: either close the app by double-clicking the Home button and swiping the app upwards off the screen, or by tapping Updates (or any other button) ten times in the App Store app.
If that fails, try turning wi-fi on and off.
If that also fails, sign out of iTunes and back in (tap on your account at the bottom of the 'Featured' page).
Next option: hard reset (hold Home button and sleep/wake button till it resets - assuming you're on an iOS device).
More severe option which will require signing back into wi-fi, etc.: Settings - General - Reset - Reset network settings