Reading the keyboard
Under each scale is the whole bells keyboard: the naturals in front, the sharps and flats in the raised row behind, low notes on the left. The filled bars are the notes in that scale, named the way the scale spells them, and the starting note has a thick outline. Find the bars before you play.
How each scale is laid out
Each measure of the scale starts with a quarter note on beat one, then eighth notes, up and back down. The arpeggio follows in triplets, and the scale ends on a whole note. With 2 octaves on, a scale that won't fit on the instrument you picked is printed in one octave and marked "1 octave". Tap a note or play a line to hear it in the instrument's octave: bells sound two octaves above the written note, xylophone one octave above, and marimba and vibraphone as written.
Natural, harmonic, and melodic minor
Natural minor uses only the notes in its key signature. Harmonic minor raises the 7th note, going up and coming down. Melodic minor raises the 6th and 7th going up, then comes down as natural minor, so its keyboard shows both versions of those two notes. Coming down, the 6th and 7th each have a courtesy accidental, a reminder that they're back to the notes in the key signature.
Practicing scales on mallets
Use a metronome and start slow. Strike the center of each natural bar, and the near edge of the raised bars when the center is out of reach. Keep your eyes on the music and use the keyboard as a map, not a crutch: by the time a scale is fast, your hands should know where the bars are.