Bokeh is the background blurred effect created by being out of focus, using a wide aperture.

This image was taken using a 35mm lens 2.8 aperture.  Notice the trees and the motorcycle headlight are all out of focus, yet the subjects are in clear focus.  That’s the art of getting bokeh by using a wide aperture. Unfortunately, the better the bokeh – the more expensive the lens.

Remember when using a wide open aperture focusing becomes difficult.  The wider the aperture the narrower the focus field.  At 1.2 or 1.4 you’re dealing with inches on a horizontal plane.  Sometimes pinpoint manual focusing is necessary through using Live View – if using Canon 7D.

Practice, practice, practice.