Once you have your business idea in place, you should decide the name of your business. I suggest you only choose a name which is not bought already and has a .com available.
1. See if a name is available. Go to who.is and enter your desired name. If its registered you may be able to buy the name, though it will probably cost a few thousands. If you have a few names in mind try them until you find one which is not taken.
2. Once you find a name which is free, go to name.com. There are other registars, but I recommend name.com for their ease of use.
3. Buy the domain. (Doh!)
4. Setup email for your new domain.
5. Buy a hosting package from webfaction.
7. Create pages for the homepage, about, what you do and a contact page.