In this video lesson, the teacher explains the meaning of the idiom "to feel like a fish out of water" using context clues. The teacher emphasizes the importance of understanding idioms as phrases that don't mean exactly what the words say. By analyzing the surrounding words and sentences, the students can infer that feeling like a fish out of water means feeling out of place and uncomfortable in a certain situation. The teacher also suggests drawing a picture to help visualize the idiom and its meaning.