Most drummers have a good knowledge of rhythm and note values but many don’t know much about reading notes of different pitches.
Music is made up of three basic elements - rhythm, melody and harmony. You have already learned the basics of rhythm in this book. Melody is a succession of notes which are sung or played on an instrument. Harmony means other notes which accompany the melody. A good example of harmony would be a guitar or keyboard playing chords.
There are several tuned percussion instruments which are capable of playing melodies and chords. These include the xylophone and the vibraphone. Even if you mainly plan to play drums, it is a good idea to learn a bit about the other elements of music so that you can understand the terms other musicians use when they are talking about their parts.