You can share citations with other Mendeley users using Groups. There are three kinds of groups:
Private: members of private groups can share references and pdfs. All group members can add pdfs and annotate them - these annotations will be visible to other members of the group. Private groups are not visible to the general public, and members join by invitation from the group creator.
Invite-only: The groups can be viewed by the public, but membership is by invitation only. References can be shared, but documents files cannot.
Open: these groups can be viewed by anyone, and anyone can join. References can be shared, but documents files cannot.
You can create your own group, or search for existing groups that cover your areas of interest.
Important Note About Groups:
You cannot change a group's type after it has been created. For example, a public group will always be public.