This dialog box appears when you click Add in the SharePoint Sites dialog box, that is in turn accessed from the Open from SharePoint dialog box. It lets you specify a new SharePoint site to be added to the list of available sites. Choose whether you will specify the name of the server and a top level site or a full URL.
To specify a site name, provide a server name, select either a normal http\\ protocol or an https\\ secured protocol using the Secure Server checkbox, and click Connect. Type in your user name and password if SharePoint prompts you to do so. When connected, the Site Name selection box will offer all available site names; select the desired one.
To specify a precise URL, it is easiest to browse to it through your internet browser, copy the URL and paste it into the URL text box. Click Connect. If the connection succeeds, you can type the display name of the selected site.
You can choose a selected site as default, so it becomes the one offered whenever you interact with SharePoint.
See DMS overview.