There are many songs that can be played with just one octave scale musical instruments e.g. xylophone, glockenspiel, ocarina, toy piano, kalimba, Kong saxophone, Kong clarinet, Kong low flute, steel tongue drum etc. If you are learning to play simple tunes on a one octave only musical instrument or starting with one octave songs with a chromatic instrument, you will find some nice sheet music here.
The simplest one octave instrument like the xylophone (picture above) plays one natural scale tones only from 1, 2, 3, 4, 5, 6, 7, 1 from left to right. However, a full one octave scale has 5 more tones or semi-tones (sharps and flats in black) in between 1 and 1. Note that we use bold 1 for the higher 1 tone.
One full octave scale as in a mini piano below.
If you play the white ones only from left to right, it is the basic do, re, mi, fa, so, la, ti, do. Some songs (few) may use 1 or 2 semi-tones (as in black), the most commonly used one is 6#. So to show the difference between the white 6 and black 6 for example, we use 6 for white, and superscript 6 (e.g 6 ) for black for # (sharp) in our music notes here.