Open up the help topics (Help, Content) and search on setbacks. The first topic, Lot Setbacks, is a good place to start. You’ read this in the second subsection down.
Lot / Parcel Traverses
Lot setbacks only apply to Lot/Parcel traverses. These are traverses that you have placed in either the Lots or Parcels traverse group. Once a traverse has been placed in this group, TPC allows you to edit setback, location and LandXML parcel data for that traverse.