Enabling my client to send html formatted mass mail

I know you've heard it all before but I will reiterate.
Your documentation leaves a lot to be desired.
I know the process is probably a lot simpler than I can grasp, but the paradigm you've created around UniversalEmail has got me pulling my hair out.
I cannot grasp how I would enable my client to have the ability to send a mass mailing of a simple one page flyer in an html email, not as an attachment.
I've gone through the various help docs over and over again but they're so generic as to be unusable for me (and others too).
I'm not alone in wanting to see something more structured i.e. "to enable your client to send html mail to his clients, you need to
1. do this
2. do that
3. do this again if
4.etc."
We've developed a printed flyer for a client he is physically mailing.
He wants to send that flyer as html mail to around 600 clients. I know I can do this with UE but I've lost my way a dozen times trying to make this work.
I imagine that I would give him a page (not publicly accessible, possibly password protected) that he would go to and hit send. At this point I am confused as to What he is sending when he hits send. Is it the page he's on or is it another (possibly dynamic) page?
I imagine too that that page could allow him to choose to whom to send from a db of clients or to individuals as well as a selection of various content.
Please help.

Mick