Migration Assistant- How easy and how much?

Hi folks, about to purchase a new iMac (currently have a 2007 model) and would like to continue seamlessly with the way I was working. I understand that Migration Assistant will (I think) do what I want to do but can anyone tell me in simple steps (sorry) exactly how I would go about doing this from the moment I put the old and new machines side by side on the desk? My other dumb question is will migration assistant preserve my rather extensive folder structure that I have within Mail? It contains my whole life really!!! Backed up in Time Machine of course but does MA recreate exactly what I have on the new machine?

Thanks again for all your amazing knowledge.