The potential at a point is defined as the amount of work done in bringing a unit positive charge from infinity to that point.what does this means?

Suppose if we  raise an object from ground to a certain height then the work we do against gravity is stored as PE in the body.

So every time we do some work on a body against some force is stored in it as energy.

In case of electric field, potential at point say P in the electric field willbe:

The influence of the charged conductor A is felt upto the bigger circle shown.

To bring any charge to point P we need to work against the electric field of the chaged A.That work will be stored at P .Potential of point P will be the work done in bringing every unit charge (+ve)to  P.