If you mean how can you put two or more of your own hubs into a group then
click on your account in top right hand side of page
that will take you to a page with a black box of choices on lefthand side (starting with statistics at the top and groups down the bottom) click on groups
on the new page that brings you to click on Add new group in the box titled your hub groups.
type into pop up box name of group and click add group
this new group will now appear in box your hub groups
until you create a group all your hubs are put into "orphan hubs" to move hub from orphan hubs to new created hub group just click onto hub you want to choose and drag into new group.
Hope that all makes sense if not just message me any questions and i will try and answer best I can.