to do this you need to add a CMS (Content Management System). There are several options and they will need some research on your part to see what works. The options I am aware of are:
Joe Workman : Total CMS and Easy CMS
Yuzool Themes : Dropkick CMS
Nimblehost’s : Armadillo
Stacks4Stacks : DropCMS
There may well be others but I don’t know. They vary in complexity and cost. Sounds like you need a basic solution.
As far as a blog solution - again there are several. Here’s a thread from last year which should help: Blogging in Rapidweaver.
Obviously a blog doesn’t offer the page layout flexibility of a CMS but it could work for you.