What is your definition of a Creed?

I don't understand the logic of Christian creedalism... eg. if you believe God's son Jesus died for your sins, you'll go to eternal heaven. If you instead believe God's daughter Jessica died for your sins, you'll go to eternal hell. If you take the creed of the Orthodox Church, you're a true christian but if you take the creed of the Protetant church you're not a true christian.