You can go about it in the following way:
1. Register the domain name (with domain registrar like dotcanuck.ca). ~$15 or so / year
2. Order hosting from any hosting company (I use sureserver) ~ $10 /month
3. Dowload Drupal or WordPress (free, as in beer)
4. Install using their guides (very easy)
5. Download and modify a theme for your site from Drupal or WordPress
6. Download the shopping cart module and install
7. Set yourself up as a vendor with M/C or Visa or use PayPal.
8. Add content and advertise
It's easy to do, there is tons of support for Drupal. You can ask on their forums (drupal.org). WordPress is mostly for bloggers, so I'd suggest using Drupal (proper CMS - content management system). It will set up a database, users with permissions and take care of the HTML portion of the business for you.
Have fun with it!
Tom
P.S. There is a lot of technical people out there that will charge you minimal amount <$1k to get this all arranged for you if you don't ask for too much customization. It could all be done within a week, up and running! P.M. me if you want more information.