You will access your eBackpack account by going to your personal eBackpack website. When you create an account, you are able to select your domain.
www.MrBMath.eBackpack.com (MrBMath is the part you set up for your account)
Your domain can be found in your welcome email as well. Be sure to bookmark this site for future use as well.
You can sign into your account on any eBackpack app as well (Windows 8, Android and iOS) by typing in your Account Name (accountname.ebackpack.com), Username and Password.