Notes and Scales
Musical notes, like all sounds, are made of sound waves. The sound waves that make musical notes are very evenly spaced waves, and the qualities of these waves - for example how big they are or how far apart they are will affect the sound of the note. A note can be high or low depending how frequently one of its waves arrives at your ear. When scientists talk about how high or low a sound is they talk about frequency. the higher the frequency the higher the sound. Frequencies can be measured like 440 vibrations per second.
People have been making music long before we knew what sound waves and frequencies were. So when musicians talk about how high or low a sound is they talk about the notes pitch. And instead of numbers they give each pitch a letter name like "C". Musicians call a note with 440 vibrations per second "A".
Octaves are the same note name but at twice the frequency. So "A" at 440 VPS is an octave lower than "A" at 880 VPS. Notes in different octaves are so closely related that when musicians talk about the not "C", it doesn't really matter which "C" they are talking about. Because of this most discussions of music theory don't bother naming octaves. Informally musicians may talk about "middle C" or "G above the staff".
The staff: The staff is written with five horizontal parallel lines. Most of the notes of music are placed on or between these lines. Extra lines can be added if a note falls above or below the staff. Vertical bar lines divide the staff into short sections called measures or bars. A double bar line is used to mark the end of a larger section of music including the end of a piece which is usually a heavy double bar line.
The most important symbols on the staff are the clef symbol, the key signature and the time signature. these all appear at the beginning of the staff.
Many different symbols can appear on, above or below the staff. The notes and rests are the actual written music. a note stands for a sound and a rest is silence. The clef, time signature and key signature tell you very important information about the notes and measures. Symbols that appear above or below the music may tell how loud to play, how fast it goes or even how to play a particular note.