Contacts can be added by clicking the Add New Contact tab in the sidebar menu. This opens up a window in which the User can input all of the relevant information that they have collected about the Contact. The fields in this window are determined by the Administrator when they are setting up their organization's database.
Contact's can be added to a particular event or tag, and assigned to a User directly from this window. Alternatively, they can be added to an event directly from the event page, or assigned to a user from their personal profile page.