Make sure that you are signed into Mendeley Reference Manager in either its desktop or online version.

Navigate to your Library, and, along the left-hand side, you will see a Groups section.

You can create a new group simply by clicking into the New Group field and typing your group name and then pressing enter.

The group can be managed, renamed, or deleted by clicking the three dot menu to the right of the group name.

Within Manage Group is where you can invite other members to collaborate on the group library. In Mendeley you have 24 other invitations to send to collaborators. Remember to send the invitation to the email address(es) that your collaborator(s) will be using with their Mendeley account.