EndNote

To create a group:

1. Select Create Group from the Groups menu.
2. A group temporarily named New Group appears on the Groups Panel.
3. Type a Group name.
4. Drag and drop selected references from All References (or from another group) to your new Group.

Individual references can be both dragged into groups and deleted from groups, noting that they will always remain in All References until deleted from there. You can drag-and-drop the new group to any custom Group Set.

You can create a Group as follows: Open an EndNote library and click on Groups at the top of the screen.

On the left of the screen a window appears in which you can type the name of the new group.

You can also find the new group there.
References can be placed in this group by selecting references and then clicking Add References to under Groups. 
Then choose the group where you want to place the references.
You can also choose the method of 'drag and drop' to add the references to a group.
Your groups are visible on the left side of the screen.