When you select a component with electrical, duct, or pipe connectors that is not a member in a system, you can create the appropriate system.
When a component that is not a member in a system is selected in a building model, the ribbon displays a Create Systems panel. The specific tools on this panel depend on the component and the types of connectors in the family. If there are multiple connectors of the same type and you want to connect to a specific connector, you can right-click the connector control 
to create the appropriate type.
Electrical
When a component with an electrical connector is selected, the Create Systems panel displays one or more tools, which allow you to create a specific electrical system: Power, Switch, Data, Telephone, Fire Alarm, Nurse Call, Communication, Control, Security.
Duct
When a component with an duct connector is selected, the Create Systems panel displays the 
Duct tool, which allows you to create a specific HVAC system: Supply Air, Return Air, Exhaust Air.
Pipe Connector
Pipe connectors are used with hydronic systems, plumbing systems, and fire protection systems.
When a component with a hydronic pipe connector is selected, the Create Systems panel displays the 
Piping tool, which allows you to create a specific hydronic piping system: Supply, Return, Other.
When a component with a plumbing (pipe) connector is selected, the Create Systems panel displays the Piping tool, which allows you to create a specific plumbing system: Sanitary, Domestic Hot Water, Domestic Cold Water, Other.
When a component with a fire protection (pipe) connector is selected, the Create Systems panel displays the Piping tool, which allows you to create a specific electrical system (from left to right: Fire Protection Wet, Fire Protection Dry, Piping Other).