To be able to communicate with other users of the software, you are able to send them notifications. Notifications are stored on the server until a client connects and synchronizes. Thus notifications can be read and deleted off-line, but to send new notifications the client has to be online.
The single most important feature is being able to ask people counter-sign your documents. You can also just ask them to have a look at a document (for whatever the purpose might be). To do so, first ensure you are connected to a server. Then select a number of documents in the view. Finally:
Menu: Document → Ask for signatureTo read notifications, look at the Notifications-tab. You can immediately see how many notifications you have within the parentheses (...).
To see which document a notification refers to, you can select one or more notifications and they will act as filters. You can open a notification by double-clicking it or selecting it and pressing Open. If you have for example a signature request, this causes the relevant document to be opened.
Once you consider a notification taken care of, select it, and press "Dismiss".