A basic look on how to read sheet music as it relates to the piano (or keyboard). What a staff is, treble clef, bass clef, time, middle C, etc. etc. Once someone knows how notes are written, they can then go on to apply it to pretty much any other instrument.
We can start with middle C, and learn a basic scale (an octave), and what a treble clef is, a bass clef, and what the corresponding notes are, and work our way to a simple piano piece.
I've been playing the piano since I was 8 years old, and I taught myself how to read sheet music. Nowadays I mostly play just for kicks in my downtime. I also play the guitar (a little bit) and even dabbled at the recorder for a while.