Okay, so we're going to talk about ancient church councils. These were big meetings that happened a long time ago, where a bunch of really important people from the Christian church got together to talk about important things.
Now, there were lots of different councils over the years, but the ones we're talking about today are the ones that happened before the big Ecumenical Councils. These were meetings where lots of bishops (who were like big bosses in the church) would get together to talk about what the church believed and what it should do.
At these meetings, they would talk about things like what the Bible said and how the church should deal with different problems that were happening at the time. They would pray together and talk about what they believed God wanted them to do as leaders of the church.
One really important council that happened before the Ecumenical Councils was the Council of Nicaea. This one was held in the year 325 AD, which was a REALLY long time ago. At this council, the bishops talked about a guy named Arius, who was teaching some things about Jesus that the bishops didn't agree with. So they talked and prayed and studied the Bible, and eventually they wrote a statement of faith that said what they believed about Jesus. This statement became known as the Nicene Creed, and it's still used by lots of churches today!
So, basically, ancient church councils were meetings where really important people from the church got together to talk about big things and figure out what they thought God wanted them to do. And sometimes, they would even write down what they believed so that others could know too!