The energizer pushes this energy from the outbound (positive, fence) terminal in very brief, high voltage and high amperage pulses, The ground terminal's (negative, earth) purpose is to absorb as much of the pulse energy as possible back into the energizer.
An electric fence is the extension of these two terminals (fence and ground/earth).
The inbound terminal is extended by driving metal rods (ground rods) into the soil and connecting them to the earth terminal with conductive wires to it.
The outbound terminal is extended by attaching conductive wires to it. They are suspended above the soil and kept separate from the soil by insulators and/or nonconductive posts.