This is a big request. 

Start with building your Connectors. Help | Connectors | Autodesk Work through the sub-categories, especially breakpoints as this is critical to building your flanges. If you already have the connectors built, then setup a new specification and assign your services to use those specifications. Help | Specifications | Autodesk. The <= is the longest side to setup < 12" duct width and height = S&D, > 12" duct width and height = TDF etc.
You can then assign your specifications to your services. The Autodesk help wasnt great for this section, hopefully this will help. Create a New Service in Fabrication CADmep Database (imaginit.com)

Get yourself signed up on xtracad.com its a dedicated fabrication web site full of information.