So picture an electric circuit on a table, then visualize voltage at various points around the circuit as the height. The higher the voltage the higher the height. Just like height you need a reference point from which height is measured. This reference point on maps of the earth is called sea level. The reference point in your electric circuit is called ground or common.
Voltage is the energy per electric charge, it is measured in volts per coulomb.
Height is a measure of the energy per unit mass it is measured in meters or alternately in joules per kilogram. So height gives energy per unit mass and voltage gives energy per unit charge. They are similar. So, if you model one part of an electric circuit as a waterfall then a high waterfall models a high voltage difference, if a lot of water flows over this high fall, then it models a high voltage circuit with a lot of current. If a small amount of water goes over a high fall it models a high voltage circuit with a little current.