From Nikita’s point of view, her "System Messages" information box alerts her that Linda wants to chat with her. She can reject Linda’s request by ignoring the message, or she can accept the request (which she does) by clicking on the blinking lights against Lindas name in the "Connected Users" list. Linda is added to her "Connected Users" list with all options set. (by default) If Nikita wants to send only audio or only video to Linda, then she can just toggle on the options.