When you first use EndNote Online you will need to set up groups to organise your references. Click the Organise tab. When importing references you will be prompted for the group that you would like the references added to.
To create a new group click the New Group button
Depending on your security settings you may need to click the security warning bar to allow scripting and adjust trust preferences in your browser.
Adding references to a Group
To add references to a group return to 'My references', tick the references to be added to a group and select the group they are to be added to. These references will always also remain under the 'All my references'