How to Use Mailing List [5.1.0]

I just discovered the "mailing list" menu in Community, and to be honest, it's not what I would all a "user's friendly" interface.

Here is the question I asked to myself, and should many users will also ask to themselves:

I can create new mailing lists, but how can I select the recipient group?
When sending email to an individual user from User's list, this mail appears in "Mailing List" menu, with "Not processed" status : weird that an individual email appears here
I don't understand when does In-Portal decides to send finally the mails
I don't see any list in "Email queue" tab, while my mails are mysteriously sent

May the system is very logical once you'll teach me, but for sure the "usability" for an average user is non-existent.