They are the way you manage your Qubes. There are two types: Public and Private.
Click a Qube, drag to the Collections zone at the beQbe left side and drop on "+" button.
Now, put a name to your collection and select the privacy: Public or Private.
To create your collection, write a title and choose privacy: Public or Private
"Manage" button is present in all Qubes which are subscribed or created by you. To create a new collection click "Manage" and "New collection" in the pop-up window. Finally select between "Public" or "Private" options.
Click on "Manage" button to choose the collection in wich you want to include your Qube.
Change the privacy of the collection
To change the privacy of the collection from public to private or viceversa, you only have to enter the collection and "Edit Collection" and after choose privacy.