When you have reached a certain level of maturity...most people will need some help with near vision.  The lens inside our eyes naturally becomes less flexible as we age.  The flexing of this lens is what allows our vision to focus from distance to near tasks.  For most people they begin to notice this change in their early 40's and it continues to get a bit worse as you progress thru your 40s and 50s.  In bifocal glasses there is a distance area of the lens up top and the reading area down lower.  It has to work a little differently in a bifocal contact lens because we can't move our eyes to look thru different areas of the contact lens.  The contact lens moves with our eye and stays centered over our cornea.  Each company that makes bifocal contacts has a little bit different technology but basically there are rings of distance and near vision in the lens.  

What to expect from bifocal contact lenses

The goal would be to achieve comfortable distance and near vision that reduces the need to put on reading glasses over top of the contact lenses for near work.  Most people who wear bifocal contacts notice a slight compromise to the quality or sharpness of their vision vs the clarity that can be achieved with spectacle lenses or single vision contact lenses.