When you start a business you have a choice: You can form a limited liability entity (such as an LLC or corporation), or you can file a fictitious name statement (also known as a DBA), which simply lets people know that you are running a business under a name other than your own.

Note, though, that the DBA is not an entity--your personal assets are totally exposed and available to creditors if they get a judgment against you. You generally don't need to file in more than one state unless you plan to have an office presence in multiple states. However, working with clients from multiple states could have tax implications, so be sure to speak to your accountant to make sure you're handling your transactions and collecting sales tax appropriately.