The lesson focuses on levers, a type of simple machine integral to many tools including those in the human body. It explains the three classes of levers: first class (fulcrum in the middle), second class (load in the middle), and third class (effort in the middle), using examples like seesaws, wheelbarrows, and rakes. A mnemonic device, “FLE 123,” is introduced for remembering the classification: Fulcrum for first class, Load for second, and Effort for third.