The Go-Around mode transitions the aircraft from the approach mode to a climb away from the ground. With the autopilot and autothrust systems selected, the Go-Around mode is available on the approach from a height depending on the aircraft manufacturer, but typically at 1500 ft.

The decision height is the height on the approach at which the pilot must see the required visual reference to continue to land. The visual reference is basically either the physical runway, its markings (paint) or an element of the approach lighting. In real life, it will be the lights that will shine to find you first.

If the required visual reference can not be established at DH, then a Go-Around will result. However, the Go-Around mode can be selected above DH if needed and infact even once landed. For example, on the B737 the mode remains available up to 2 seconds after touch down.

Note: Go-Around basically tells the autopilot to pitch up with wings level and the autothrust to select a high thrust setting for climb out. The pilot must retract the gear and flaps as practical.