Reddit mentions of How to Read Music: Fundamentals of Music Notation Made Easy

You'll find that sheet music is superior. Its only complicated because there's lots of things to tell you. Each note in standard notation tells you how long to hold a note, the timing of the song and how to "count" the beats... as well as the pitch. Lots and lots of information in the sheet music.

Unfortunately, learning sheet music will take some time. I would suggest buying a beginner songbook with tabs AND sheet music to assist you in your studies. I personally found this book to be useful. Its filled with beginner songs in both tab AND standard music notation.

You'll still need another book to learn how to read. There's more to music than just pitches. You need to learn timing (ie: the difference from quarter notes and eighth notes) How to Read Music is very dense... it covers a lot of material in a short amount of space. I liked this book, although some other people may prefer maybe a slower-paced book.

Finally, you'll need to know the location of the notes on your harmonica. These charts will tell you everything. If you have a C Harmonica use this chart.

The combination of a sheet-music beginner-level book (to practice with) PLUS your tutorial book should be enough for you to get started. Good luck.