If you play a string instrument and want to learn the notes on each strings, the notes on music staff, etc. the FretTrainer APP is good. There are 6 instruments available to practice on: Guitar, Bass, 5-String Bass, Mandolin, Ukulele, Banjo.
This is an excellent and short tutorial on how to read music. It is only 5 minutes long and offers a good foundation to get started reading music. It is short enough that you can (and should) watch it several times until you understand it.