Varifocal or progressive lenses allow you to see in the distance and close up with just one pair of glasses. There are no visible lines or markings on the lenses as there are with bifocals, so cosmetically they appear to be a straight forward lens.
As you look through the top of the lens you are able to see comfortably in the distance, and as you look down towards the bottom of the lens through the reading part, close work comes into focus.
All varifocal lenses give some distortion towards to edge of the lens due to the amount of technology that is need to incorporate a distance and reading prescription. There are many types of progressives on the market, and the general rule is that the better quality the progressive is, the more comfortable your vision will become.
With a basic progressives you may find that you have to turn your head or adjust your position in order to bring your vision into focus, where as with a customized progressive designed specifically for your eyes and frame choice would give a much wider field of view.