How to set up a multi-site environment?

I want to convert an old html health-related site to wordpress, along with my blog site sharons.org.uk The blog is already on wordpress and is working very nicley, but I have fears and trepidation with regard to my other site. I know that I can create it all in the background and then go live and publish it all in one go, but I am unsure about the process of setting up the multi-site. I don’t want to delve into wordpress’s html if it can be avoided, and that applies to php more so. Can anyone suggest a site which has a good tutorial in, with the work-flow being A->B->C, etc please? The current situation is, afaik, ‘Domain [hosted by 1and1] sharons.org->wordpress, main site separate from blog and wordpress, historically created first.

Thanks
Sharon.