Motorized valves come in two basic forms, 3 port or 2 port.
3 port valves are used to share the flow of hot water from the boiler to the heating circuit and to the hot water cylinder.
2 port valves are often referred to as zone valves. These are used to control individual circuits. A 2-port valves looks very similar but without the bottom pipe forming the leg of a T.
Generally they have a brass body with a metal or plastic power head fixed to the top with a wire flex attached.