The Catania 6-Note Kalimba is a rugged instrument, great for children or for music therapy. It is economical, can be tuned in many ways, and can play a surprisingly large repertoire of songs for a kalimba with so few notes.
The pentatonic scale has five notes in an octave, and the 6th note is the same as the lowest note, repeated at the top of the scale. There are actually many possible tunings of the 6-Note Pentatonic Kalimba, but right now we'll just look at the three tunings that are used in the 6-Note Booklet - the standard C tuning, the F "5" Tuning (because it has the 5 in the bass, or lowest note), and the G "5" Tuning.
The numbers 1, 2, 3, correspond to the notes of the major scale, "Do, Re, Mi", etc. In the major pentatonic scale, the 4th and 7th degrees of the scale are missing. In the standard tuning, the lowest note C is the root note, or "1". However, by tuning the 3 note up just a bit, from E to F, and calling it the root, the notes form the F major pentatonic scale, but with the 5th in the bass as well as at the top.
The tuning of your kalimba determines the songs and the sort of music you can make with it. That is especially true when you only have six tines. The standard C tuning for the 6-Note Pentatonic Kalimba can play a few songs you know: Joy to the World (Jeremiah Was a Bullfrog), Swanee River, Oh! Susanna, Shortnin' Bread, and the guitar riff from Sunshine on a Cloudy Day.
In the F or G "5" tunings, there are actually many more songs you can do - Amazing Grace, As I Went Down to the River to Pray, This Little Light of Mine, and She'll Be Coming Round the Mountain When She Comes. These songs form a family of related melodies that usually start on the 5th and swing up to the root note or 1 - as in This Little Light of Mine = 5 6 1 6 1.