Do you have to give credit to the source when you teach what you learned from someone else?
No, credit to a human source is not required when passing on biblical teaching. The emphasis is on using Scripture and recognizing that God opens the heart. A teacher may present what they learned as though the Lord revealed it, provided the Word itself is used. The instrument matters less than God's work.
In the supplied unit, Les explains that no minister or teacher can accomplish anything unless the Lord opens the heart, using Lydia in Acts 16 as the example. God opened her heart, but He used Paul as the instrument. Les applies this same pattern today and says he appreciates prayer for those who pass these things on. He tells people that if they take what they have learned and teach it, they do not have to tell their class where they got it or give him credit. They can teach it as though the Lord revealed it to them, as long as they can use the Scripture. He stresses that the main thing is being instruments God can use when He opens a heart so somebody can give Him the Word. He also notes how seldom people claim salvation entirely by themselves without outside input.