Invitation to Portal

Now that the invitation functionality is available in the new application portal, I am wondering how to go about using it? We send about 100 invitations per quarter to specific contacts on organizations currently, by pasting the unique program link into an email document template. We like that this creates a document and activity record that we can track, but it is not very attractive from a user interface perspective and the Invitation communication from the Program email side would look and feel more streamlined. However, I am not sure how to send them, and I am not sure how to track them. Does anyone know, and is there documentation anywhere? Haven't been able to find anything so far.