Here are two short answers about what the opt-out and public option means, as they say in lay-men's and -women's terms.
As Josh Marshall over at talkingpointsmemo puts it:
I have what I think of as a decent layman's understanding of health care policy questions. But since the idea was floated early this month I've made an effort to canvass the views of the people who I consider most knowledgeable on these questions. And I think I'm on solid ground in saying that there is a consensus among the people who understand these issue best on the reform side that this is a good pragmatic compromise that may not be perfect but gets you most of what the public option concept is meant to accomplish.
Or as Anna Quindlen puts it in a review of the Obama presidency's incrementalist approach in next week's issue of Newsweek:
(By the way, if you're confused about the public option, just ask yourself this question: would you like to be eligible for Medicare at 40 rather than 65?)