Contacts contain list of persons and groups of persons in directory. If you click the button contacts, a context menu will unroll, which contains a command for new contact addition.
If you double-click on any contact, you will call up a dialog for writing new message to the selected contact (person).
Each contact has also context menu with commands for writing new message, modifying contact's properties, searching for persons and addition/removal of the contact.
For further information, see directory.