Music notation is the written language of music. The ability to read and write musical notation allows musicians, regardless of genre or location, to effectively communicate their music to one another. As with any language you don't understand, music notation appears to be difficult to comprehend, but in truth, learning to read and write it isn't that difficult.
Music Theory Books
A plethora of music books are available that teach the fundamentals of music. It's a good idea to have one and keep it handy, not only as a means by which to teach yourself how to read musical notation, but as a reference source further down the line. You don't need a library of books on the subject. One good book will do. "Music Theory for Dummies," published by Dummy Books, and "Music Notation," published by Crescendo Books, are two books that will suit the beginner well.
Music Theory Online
The Internet provides a wealth of basic music websites aimed at helping you teach yourself the fundamentals of reading music. The hardest part is choosing which of these many websites give reliable information. DataDragon offers a comprehensive music notation database that can help you learn how to read music (see Resources). The Violin Case website has free online flashcards that allow you to name notes on the treble clef and score your progress. The Basics of Reading Music (see Resources) will get you off to a great start.
Study Sheet Music
Use your music-reading skills as you learn them. The best way to do this is to read sheet music. If you can play any instrument, use that skill along with your newly-acquired note-reading skills. Purchase sheet music in a music store or find many free sheets online (see Resources). Starting with simple sheet music is best, then you can work your way up to more complex scores.