The End Connection command inserts a diffuser connection that extends from the end of a duct directly to a diffuser. The connection is inserted as a straight line. No additional turns or adjustments to the duct path are inserted.
To insert an end connection, go to
Ribbon: DM HVAC->Diffuser Connections-> 
End Connection
Pulldown Menu: DM HVAC->Diffuser Connections->End Connection
You will be prompted to specify the diffuser to be connected.
Select diffuser to connect:
You will then be prompted to specify the duct to which the diffuser will be connected.
Select duct or label to connect:
A connection will be inserted from the end of the selected duct to the diffuser.