How to define groups in OH2

Can anyone advise how to define groups in OH2
Habmin presents a groups field in the edit item window but changes to this field don’t stick.

It appears that in OH1 this was done in the item configuration file but I don’t have one. All my items were automatically created or edited in a OH2 UI.

First, disable “Simple Mode” in Item Linking in your Configuration -> System via the Paper UI
Then on the left menu the Items sub-menu will appear under Configuration.
There you can add a Group (select type Group)

By the way: you can still use the items configuration file (create a new one) and put there your items and groups