You'll need a Username and Password to be able to edit your business site. Your Username will also need to have permission to access your business site. If you don't already have one, you can create a Username from the Sign-In screen, but you will still need to have your business claim set up before you can change things. This is a security feature so that only an authorized representative of the business can change the content of your site.

More on 2. Sign In.