In this lesson, the focus is on understanding musical notation through concepts like tonality, key signatures, and accidentals. The lesson explains that accidentals are notes that deviate from the standard scale, such as sharp and flat notes, which are typically the black keys on a piano as opposed to the natural notes on the white keys. The use of sharp notes is highlighted through examples, such as the iconic Jaws theme, illustrating how they modify the pitch and bring dynamics to music.