What gets lowered
Against a major scale on the same tonic, natural minor flattens three degrees: the 3rd, the 6th, and the 7th. The lowered 3rd is the big one. It is the note that flips the scale from major to minor, and it is the first thing to listen for. The lowered 6th and 7th do quieter work: they pull the top of the scale away from the octave, so instead of leaning home the way major does, natural minor settles in sideways.
The step pattern is W H W W H W W. Notice the half steps land between the 2nd and 3rd degrees and between the 5th and 6th, different places than major, which is exactly why the two scales feel so different even though five of their notes are shared.
The relative-minor trick
Natural minor and major are two views of the same set of notes. The white keys from C to C are C major; the same white keys from A to A are A natural minor. They share a key signature and every pitch. Only the starting note, and so the center of gravity, has moved. That is what "relative" means: A minor is the relative minor of C major.
The practical shortcut falls out of this. The 6th degree of any major scale is the tonic of its relative minor, which is three semitones down. It is worth internalizing because it means every minor scale you learn is a major scale you already know, re-centered.
On the staff
The missing leading tone
The single most useful thing to hear in natural minor is what is not there. Major and harmonic minor both have a leading tone, a 7th degree a half step under the octave that strains upward into it. Natural minor flattens that 7th to a full whole step below the tonic. The approach to the top of the scale goes slack. That looseness is the tell: a minor scale that arrives at the octave smoothly, without a final half-step snap, is natural minor (or the descending side of melodic minor, which is the same thing).
Kostka and Payne suggest a cleaner way to hold the three minor scales in mind: think of them as one minor scale with a variable 6th and 7th. A composer raises or lowers those two degrees as a line climbs or falls; natural minor is simply the form with both left low.
It is also why so much folk and rock writing prefers it. Functional classical harmony wants the leading tone to drive cadences, so it reaches for harmonic minor. A modal pop song that just wants the color of minor, without being pulled toward a resolution, stays in natural minor.
How Aubel handles it
Natural minor is one of the two scales the Scales game starts with, alongside major. They are paired on purpose: the first skill the game trains is hearing the minor 3rd against the major 3rd, which is the foundation every later scale leans on. Rounds play the full scale up and down from a random root, so you learn the shape rather than one key. Clear the starting pair and harmonic minor unlocks next, the same scale with the leading tone added back.