Are you trying to use design line and fill or just placing parts using the service window?  Are you seeing a list of parts you can choose from?  See image below;

If you dont see this type in the command USESYSTEMS.

If you don't see the service palettes, I would recommend running the "USESYSTEMS" Command. You may have to type it in twice in order for the Palettes to display. You can also use the "TBAR" command to get the CADmep tool bar to display. This also may have to be entered twice in order for the Palette to display.

At that point you will want to select a service you're trying to work with... for example HVAC - Supply Air. Then set a section if need be or just select the straight piece of duct on the service palette. The duct properties will appear, fill those out, click okay, and you will see the duct appear on your cursor. Click anywhere on the screen and you will see the full joint piece of duct. You then will want to use the attacher arrow in order to continue drawing ducts/fittings.