The major scale blueprint
Every major scale follows the same pattern of whole steps (two frets) and half steps (one fret): W-W-H-W-W-W-H. Starting from C, this creates C-D-E-F-G-A-B-C, the notes all white keys on a piano. The major scale is the foundation of Western music because this particular arrangement of intervals is perceived as bright, stable, and resolved.
Any major scale uses the same pattern offset by a different starting note. D major follows the same W-W-H pattern but starts on D, so it uses F-sharp and C-sharp to maintain that spacing. Learning the pattern rather than memorizing every scale in every key is the shortcut to fluency.
Natural minor and its variations
The natural minor scale follows a different pattern: W-H-W-W-H-W-W. Starting from A, this gives A-B-C-D-E-F-G-A, the same notes as C major but starting on the relative minor. This scale sounds introspective and mournful. Harmonic minor raises the 7th degree (creating the A-B-C-D-E-F-G#), which allows a traditional V-i cadence. Melodic minor raises both the 6th and 7th ascending but reverts to natural minor descending.
Most melodies in minor keys blend these flavors rather than sticking to one. A composer might use natural minor for a soft verse, then add the harmonic minor's raised 7th to sharpen the chord progression, or use melodic minor for a rising melody. Understanding all three unlocks the flexibility inherent in minor-key writing.