Simplest way (what I did)
Choose a Host.
Since you want it to be very simple. Choose a content management system (CMS). I've been using
Joomla since its split from Mambo.
Its modular, which means you can add and remove "
modules" (like a transaction system, forum, picture gallery ect) when and if you need to.
Your web host will have an automated installer for Joomla (via CPanel) to make things easier.
Test it out.
Now be prepared for long nights. Making Joomla work the way you want to is a pain (well for a individual who suffers from Obsessive Compulsive Disorder, Like me it was :P)