Start by selecting a domain name (your URL). You can either register it separately with a domain registrar like GoDaddy, or you can register it with your website host. Some website hosts include a free domain registration in their hosting package. This can save you some money.
The next step is to find a website host. Decide the features you need - do you want to open an online store or create a basic website? Certain hosts specialize in certain types of sites.
Design your web pages. You can either design them yourself or hire a designer. These days, many website hosting companies offer free website design templates that you can use if you host with them. They can be very easy to use (even if you've never designed a site before), and they can produce a professional-looking website without a lot of work.
Next, if you want o accept payments from your customers online, you need a merchant account. Again, some website hosts provide this service as well. You can also set something up separately. Online payment services like PayPal can be integrated into most websites.
Lastly, you want visitors to find your site. Without going launching into the marketing topic, there are a few online marketing strategies that you can use to help you "get found." Get Website Tools.