Intervals are the amount of space between two notes. If you understand intervals, it is easier to understand the circle of 5ths AND you will play better in tune.
Key signatures are actually designed to keep things simpler in the music! Find out how they work, and why here.
How notes relate to each other, what they are worth, time signatures, and subdividing.
All the basics: reading notes (treble and bass clef), accidentals (sharps, flats and naturals), dynamics (loud and quiet), and simple rhythms.
Tips on how to read Treble Clef - For Violinists
Tips on how to read Alto Clef - For Violists
Tips on how to read Bass Clef - For Cellists and Bass players
It looks like the Alto Clef (violas) but it isn't, and you need to know how to read it!