Do you mean the Image Review feature, that displays the image on the LCD after the image is captured?
If you see the image with the histogram or shooting information superimposed over the image and you want to see just the image press the up or down keys on the Multi-selector button on the back of the camera until you see the image only. See page 123-129 in the D5100 Users Manual.
If the image doesn't appear on the LCD after you release the shutter, go into the Playback Menu in the camera and highlight Image Review. Then set Image Review to On. The next time you release the shutter, the image will be shown on the LCD. Good Luck and Enjoy your Nikons!