If you use EndNote for multiple assignments or are working with chapters for a thesis, groups can be a very useful way to manage your citations. Group Sets are like "folders" and Groups are like "sub-folders".
Create a Group by going to Groups on the EndNote toolbar, choose Create Group and name accordingly. You can then drag and drop selected citations into this group as needed.
Select (Ctrl click) References you want to put in a group.
Go to Groups – Add references to - Create Custom Group. You can rename this to something meaningful.
Groups can be deleted any time if you wish - references will stay in the All References library. Avoid deleting the individual citations as this may unintentionally corrupt any related documents.
To create a hierarchy of groups, you can use a Group Set (see PH100 example below). Find the Group Set option in the Groups menu, name it accordingly and start creating Groups under it. If you have existing Groups you would like to add to a Group Set, just drag and drop your Group name into the Group Set.