There are different ways to connect outside wiring to the live wire of a ground spot. Firstly, you can solder the wires together. Remember to protect the connection using a shrink sleeve with adhesive. Often, the wires are protected separately using a shrink sleeve and then the entire wire can be protected using a shrink sleeve.
There are also junction boxes you can use to connect to the ground spot. These boxes are filled with resin. The moulding resin ensures the connection is watertight.