When viewing a picture, the sharper parts of the image are considered more important and the blurred parts least important. If you can control which parts you would like to blur and sharpen, you can give the picture a greater visual impact.

How can I blur something while sharpening my subject?
One word: Aperture!
Yes, aperture can do it all. Opening the aperture allows more of the curvature in the lens to be revealed. The more the lens is revealed, the less depth of field you will receive (meaning less of the picture is clear, or minimum depth of field).

A small aperture will give your photograph a maximum depth of field (meaning the majority of the picture is in focus).

To blur other objects while making your subject sharp, place only your subject in the mid-ground. Placing everything else in the foreground and background will give you minimum depth of field. Here are some examples to help you understand more about depth of field by changing the aperture.

Tip: Just make sure that when you change the aperture, you align the shutter speed along with it.

Tip: The subject in the mid-ground will be in focus while the foreground and background will not.