What is "tune"?

Tune: The pitch position of the tone train formed by the interval structure of the basic scale is called the key.
The naming of the tones is based on the tonic. For example, if C is the dominant tone in the numbered musical notation 1, 2, 3, 4, 5, 6, 7 if C is the dominant tone, that is C=1, it’s natural tone level is arranged in order from C (C , D, E, F, G, A, B), this is the C tone.
In the same way, in the D key, D is the main sound, that is D=1, and there are two sharps in the key signature. The scale structure of the D key is deduced, namely D, E, F#, G, A, B, C#.
The key of F has F as the main tone, namely F, G, A, Bb, C, D, E.
G tone G is the dominant tone, namely G, A, B, C, D, E, F#.