A scale is like a staircase. In the major scale, there are eight notes going up the steps from bottom to top. These are the eight notes of the octave. On a C scale, the notes from low to high would be C, D, E, F, G, A, B, C.
But in a scale, some steps are larger than others. In a major scale, there are five whole steps and two half steps.
These steps are shown more easily on a piano keyboard: a whole step is the distance between a white key and the next white key, providing there is a black key in between; and a half step is the distance between a white key and the nearest black key. Also, the distance between two white notes that have no black key between them.
It is possible to raise or lower the pitch or highness of a note by a half tone.
The “sharp” (#) raises the pitch by a half tone. C-sharp, for example, is a half tone higher than C.
A flat (b) lowers the pitch by a half tone. D-flat would be a half tone lower than D, and would be the same sound as C-sharp.