Check Available Mac App Store Updates from the Dock
If the Mac App Store is open and there are updates available, you’ll notice a red badge appear on the icon in the Mac OS X Dock. You can then right-click on the Dock icon and scroll up to “Available Updates” to quickly check what apps need updating.
Selecting one of these apps through the Dock icon then pulls up the apps page on the App Store, although it would probably make more sense to have this launch the update for that app instead.
If you’re new to all of this, you can learn how to update apps through the Mac App Store, it’s extremely easy.