Am and A under a hand
Am
Strummed from the lowest string to the highest, this grip sounds A, C, E and A, which are the degrees 1 ♭3 5 1 rather than the 1 ♭3 5 of the written chord. The root is the lowest note, so this grip is in root position and sounds the way the written chord suggests. With A in the bass and four strings sounding three notes, the 1 appears more than once.
Strummed from the lowest string to the highest, this grip sounds C, E and A, which are the degrees ♭3 5 1 rather than the 1 ♭3 5 of the written chord. The lowest note is the ♭3 rather than the root, so this grip is in first inversion, written Am/C. It has the same notes as the root-position grip, but with C in the bass it sounds different.
Strummed from the lowest string to the highest, this grip sounds E, A, C and E, which are the degrees 5 1 ♭3 5 rather than the 1 ♭3 5 of the written chord. The lowest note is the 5 rather than the root, so this grip is in second inversion, written Am/E. It has the same notes as the root-position grip, but with E in the bass it sounds different. With E in the bass and four strings sounding three notes, the 5 appears more than once.
A
Strummed from the lowest string to the highest, this grip sounds A, E, A and C♯, which are the degrees 1 5 1 3 rather than the 1 3 5 of the written chord. The root is the lowest note, so this grip is in root position and sounds the way the written chord suggests. With A in the bass and four strings sounding three notes, the 1 appears more than once.
Strummed from the lowest string to the highest, this grip sounds C♯, E and A, which are the degrees 3 5 1 rather than the 1 3 5 of the written chord. The lowest note is the 3 rather than the root, so this grip is in first inversion, written A/C♯. It has the same notes as the root-position grip, but with C♯ in the bass it sounds different.
Strummed from the lowest string to the highest, this grip sounds E, A and C♯, which are the degrees 5 1 3 rather than the 1 3 5 of the written chord. The lowest note is the 5 rather than the root, so this grip is in second inversion, written A/E. It has the same notes as the root-position grip, but with E in the bass it sounds different.
Three shapes for Am on ukulele: Am, Am/C and Am/E. Three shapes for A on ukulele: A, A/C♯ and A/E.
These two chords differ by one note. If you find a grip where only one finger moves between them, that finger is playing the note that makes the difference.
A minor and A major differ by a single semitone in a single note, the middle one, which is called the third. Everything else is identical. On a ukulele, A minor needs one finger and A major needs two, and the second finger plays that raised third.
This is more useful than it may first appear. Once you know that one note makes a chord major or minor, you can stop learning chords as unrelated grips and learn them as one shape with a single note that changes. The two chords below share their root and fifth, and only the middle note moves.
The shapes are drawn together so you can find the grip where only one finger moves. That finger plays the third, the note that gives the chord its character.