A scale is a series of notes of different pitches that form a scheme from which a tonality is usually derived.
While there are a few different modes, the most basic one is a Major scale.
Major Scale Example
|C Major||Do, Ré, Mi, Fa, Sol, La, Si, [Do]|
|G Major||Sol, La, Si, Do, Ré, Mi, Fa#, [Sol]|
|D Major||Ré, Mi, Fa#, Sol, La, Si, Do#, [Ré]|