I was doing some research on the various church councils down through the ages and I found the above image. I found it quite helpful.
If you are not aware of the church councils, they were called to address an issue of heresy that was pervading the church at the time.
The councils acted as an arbiter of correct doctrine and belief. They discussed the issues and made a concrete decision of what is true.
The Nicene Creed is a classic example. It grew out of the Council of Nicaea and addressed the issue of Jesus Christ being equal with the Father and the Holy Spirit.
The thing I find interesting is that some follow the beliefs and teachings that the church made concrete decisions against. Some current day cults actually teach that Jesus was a created being.
If you have some time I would encourage you to have a look at the church councils and see how much we believe today is based on decisions they made many years ago.