You can organise your references into groups in whatever way is most convenient for you: by subject area, unit code, project etc.
- To create a new group, either click on Groups > Create Group from the top toolbar, or right-click on 'My Groups' in the left-hand sidebar and select Create Group

- Give your group a name and press Enter
- Drag-and-drop references from the main list on to the group name to add them to the group. (or Right Click .. Add to Group)
- NB a reference can be added to multiple groups