Where did Paul and Barnabas first preach and teach together?

They first taught together in Antioch

Source: Acts 11:25-26

What did Paul say about Bishops and teaching?

He said that bishops should be apt to teach.

Source: 1^st Timothy 3:2

How did Jesus start his teaching in the Sermon on the Mount?

He started it with the beatitudes. Blessed be…

Source: Mathew 5:1-12