Learn how to use steps to construct a musical scale. Once you know the formula for a scale, you can build the scale in any key. The steps for a major scale are whole, whole, half, whole, whole, whole, half. The last half step makes eight notes in the major scale rather than seven, but the eighth note is simply the first note an octave higher. The notes in Western music are C-D-E-F-G-A-B. Between each of these notes is a sharp are flat (depending upon whether you play the note ascending or descending. that add the notes C#-D#-F#-G#-A#. There are no sharps or flats between E and F or B and C. The distance between these notes is only a half step. The distance between all others is a whole step. Example: from C to D is a whole step; from C to C# is a half step. Following your step formula and starting on C, you get the notes C-D-E-F-G-A-B and the octave C. The name (and key) of the scale is the same as your starting note.
Learn your instrument with scales. One of the primary use of the musical scale is to play it in as many locations as possible on your instrument of choice. By playing your scale in as many locations as you can on your instrument, you not only help develop your ear to hear the different keys, you train yourself to memorize where you can find notes in different positions on your instrument.
Write songs using scales. Keeping a scale in mind while you compose helps you keep your song comfortably within a tonal framework. You build chords and write chord progressions based upon the scale you're using to compose a song. Chord progressions are typically based on movement within a scale. A I-IV-V progression, which is a common chord progression for many songs, means you use the chords built on the first, fourth and fifth notes of a scale. In the key of C, these chords might be C, F and G. Knowing the chords and notes used within the scale, even if you refer to a chart, helps you use only the notes that will go together in a song.