I don't have the d5100, but I think its the same. It is a setting, but even with it turned on, you don't need to look at it. It is invoked by your up/down arrow as you review pictures. Push your up/down control once or twice and you should get back to the normal view. In the menu, you can decide whether or not to show that info with the up/down press. Its good to have. The flashing areas are overexposed. Check your manual for more details.
