Nikon D5100 i buttonExplanation: The i-button switches the display of shooting information on the camera monitor on, just like the info button.
If the camera information is already displayed it will switch the option to change settings that are highlighted in yellow on and off.

In live view mode a push of the i-button will take you from the image preview straight to the screen for changing camera settings.

Recommendation: It is enough to get used only to this button for displaying and changing shooting information. You need the info button only to switch off the shooting information completely.