When you first start the iPhone app you will be presented with a page that allows you to use your existing SharedPlan Central account or create a new one.
To use an existing account, you'll need your Central account name, user name (email address), and password. Once you enter that information the iPhone app will fetch a list of your Central projects.
To create a new account you'll enter the name you would like for your new account, your name, your email address, and the password you would like to use. The iPhone app will then create the new account for you and populate it with a sample project to get you started.