In Mark 11:23-24, Jesus teaches about the power of faith and the importance of believing in one's prayers. He emphasizes that if someone has faith, they can command a mountain to move, and it will happen. This illustrates the idea that strong belief can lead to remarkable outcomes. Additionally, Jesus encourages people to pray with confidence, assuring them that whatever they ask for in prayer, if they truly believe, they will receive it. This passage highlights the significance of faith in the relationship between individuals and God.