The chromatic scale is made of twelve notes, consecutive from low to
high, where each pair of adjacent notes is a minor second, one
half-step. The thirteenth note would be an octave above the first
note.
The names of these notes are as follows:
C
C# (D-flat)
D
D# (E-flat)
E
F
F# (G-flat)
G
G# (A-flat)
A
A# (B-flat)
B
then the series repeats again, starting at a C.
You can begin this series at any point in the series, and cycle through
the twelve note names, then begin again. For example, yo could
begin at A, like most 88-key keyboards do, name the notes clear
up through G#, then begin again at a higher A.
The next thing is to see how to use a subset of the chromatic scale to
form more practical everyday scales that most pieces use, like major,
minor, and some of the old church mode scales.