Grouping is a method of putting items with some common characteristics in a single organizational unit. For example, let's say you ship brass pipes, brass handles, etc. If all of these items have the same freight class, you could create a group called ”Brass Items” and assign a freight class. In the future, when shipping items that would fall into this group you could select all the rows on the second page of the Shipping Assistant and set them all to the same group. When the Bill of Lading is created these items would all be specified on one line.
You can set Groups up in Maintain > Groups.