The skeleton for melodies…
Major scales are the things we use to form all scales by changing them either to modes or altered scales, and all chords either are or can be explained through scales. So getting the major scales, in all keys, is important – REALLY important. There are 12 keys for all scales, although a few of them can be written in two different ways.
The Db major scale can also be written as C# major.
The B major scale can also be written as Cb major.
The Gb major scale can also be written as F# major. In fact, but Gb and F# have the same number of sharps and flats – exactly 6.