Western music divides each cycle of the spectrum of sound into 12 semitones, or notes. This group of notes repeats, with the first appearing again (doubled) as the starting note of the next cycle, while you proceed higher and higher in tone.
1 2 3 4 5 6 7 8 9 10 11 12 - Note that 12 is the next cycle's first note. This grouping is simplified further by reducing those notes to 8 main, conveniently named notes called an octave:
A * B C * D * E F * G * A - Other notes are still between the main notes, and are called sharps or flats depending on the direction you are going. For example, from B to A there is a flat (Bb) in between them - but not from C to B or E to F.