You can create private groups for collaboration, giving you the possibility of sharing references and PDF files (including annotations) with other Mendeley users. To create a group in Mendeley Reference Manager, click on New Group under Private Groups in the menu to the left and give the group a name.
To invite members to the goup, right click on the group name and select Manage Group. Click on Invite members and enter the e-mail addresses of the people you want to invite. If they don't have one already, they will need to create a Mendeley account to join your group.
In the group you can then drag and drop the references you want to share with the group. You can create separate collections in the group by right clicking on the group name and selecting New Collection.