That is the simple plumbing to which I am referring. When you turn on the spigot connected to a water hose, the amount of pressure that you have at the end of the hose depends on how much you open the spigot. This pressure can be measured in pounds per square inch. With the spigot opened fully you will have a constant pressure at the end of the hose. The pressure can vary if you reduce the length or diameter of the hose or add a nozzle which restricts flow at the end therefore increasing pressure.
Electricity works the same way.
Think of voltage as equivalent to pressure in the water hose and the hose itself as the wire that carries the electricity. Water flowing through the hose has resistance from the inside hose surface itself as well as at the nozzle. This same resistance occurs as current flows through an electric wire. However, in electricity the resistance is measure by a unit called the Ohm . With greater pressure, water flow increases through the nozzle and resistance is greater.