After you first sign up, you'll need to wait for your Shoppe Pro store to be manually installed and configured by us, which is typically within hours, but can take up to 24 hours. As soon as your store is installed, you should receive another email titled "Shoppe Pro Store Setup". Once you've received that email, your store admin is ready for you to log in.
After your domain has propagated, you can log into your store at:
http://yourdomain.com/storeadmin (replace yourdomain.com with your actual domain, of course).