This is the grouping function, which allows you to place hubs in related groupings of your choice. You can access this function in one of two ways. The first way is to go to each individual hub, into edit mode. Check the side of the hub and you will find the following: settings, summary, advertising and groups.
Go into the groups menu and you will be given the option of placing that particular hub in a group. Choose "new group" if you don't have any now. Name the group and place that one in there.
The other way of accessing groups (which might be better for you, since you haven't started yet) is to go into your account, and find the tab that says "groups." There you will have the option to set up groups and then place appropriate hubs in them.