What is the purpose of a sump pump?
Yes, generally you'll have a sump pump if the water table could reasonably rise to the level of the bottom of the basement.

The sump pump is most often used in combination with a drainage system around the foundation that directs water into a "sump pit".  The sump pump then pumps water out of the sump pit once it rises to a certain level.  If you have city sewer service, the water is usually pumped into the sewer system.  If not, it's usually just pumped up through a PVC pipe and out into the yard.