First, install the ground spot casing at the desired location.
Make a watertight connection. The safest way to do this is by making a connection in a junction box and then filling the box with resin. The resin in the junction box ensures that both the connection and garden spot is completely sealed against water.
Secure the spot in the ground spot casing.
Consult your ground spot manual to ensure you connect it correctly. The spot connection may differ from fixture to fixture.