For my answer to the question, there are many ways someone goes about it:
Get a host that provides tools for creating a website. The upside is that it is easy, the downside is it is extremely rigid, difficult to move beyond the scope of what is provided, and the site is non-transferable to another host.
Buy a template and have it hosted wherever. The up is the site is extremely portable and easy to edit. The downside is if you need more than the template was designed for you could end up paying a professional about as much to alter it as you would have to just get a custom site.
Have a custom site designed. The upside is you can pretty much take it anywhere, provided the environment supports whatever languages the designer uses, the site will be designed with promoting the brand image in mind, and its not a big deal to increase the scope of the site beyond the initial request. The downside is the expense and the time. These sites can also have the content edited by use of an editor or through an online admin.
The editor one chooses can vary based on the environment and how comfortable someone is with current products. Microsoft offers Expression, and Adobe offers Dreamweaver. Then there are countless other WYSIWYG editors all striving to be the best. I would recommend Expression if the host offers Frontpage Extensions and the user has a good knowledge of Office products. The toolsets are similar. Dreamweaver is for those who just generally don't like Microsoft but want a well-rounded program for editing websites. Personally, politics aside, I still use Frontpage 2003 in code view. It is more intuitive than Dreamweaver's code view.
I'm trying to be complete in answering the question, but its like opening a can of worms... One aspect not talked about is creating the graphics for the site. I use Photoshop. Someone else could use Fireworks. Then there are the countless shareware programs. I wouldn't recommend the purchase of a big software set because you could spend the same amount of cash in paying for a professionally designed site, and the amount of time it takes to figure out how to do stuff could be overwhelming.
All in all though, a seldom user could be just as well served by finding a shareware program on Downloads.com to edit a single website. Just keep in mind that you 'could' build your own house, but would the end result be worth it?
EDIT:
I make a living off of designing websites. Is it wise to start up a site that sells stuff? Who knows? It could be, but you need to have a hook. It HAS to stand out from everyone else who does the same thing.
If you do a partnership, put everything, and I mean EVERYTHING on paper. From who controls what, who makes what types of decisions, to what work is expected from each and if there is a mess up what the consequences are. Beyond that, go for it. You might make a buck or two.