The C scale doesn't require any flats or sharps. It starts on the note C, then continues upward to D, E, F, G, A, B and C.
F Major uses one flat. The notes of the scale are: F, G, A, B♭, C, D, E and F.
The B♭ Major scale uses two flats, B♭ and E♭. The notes are B♭, C, D, E♭, F, G, A and B♭.
E♭ Major has three flats, B♭, E♭ and A♭. After the first E♭, the notes are F, G, A♭, B♭, C, D and E♭.
There are four flats in A♭ Major: B♭, E♭and A♭, plus D♭. The note are A♭, B♭, C, D♭, E♭, F, G and A♭.
D♭ Major has five flats, the same as those in A♭ Major, as well as G♭. This scale is D♭, E♭, F, G♭, A♭, B♭, C, D♭. The sounds these notes make are identical to those of C♯ Major, where every note is written as a sharp: C♯, D♯, E♯, F♯ G♯, A♯, B♯, C♯.
Every note is flat except for F in G♭ Major: G♭, A♭, B♭, C♭, D♭, E♭, F, G♭. This scale sounds exactly like F♯ Major: F♯, G♯, A♯, B, C♯, D♯, E♯, F♯. On a piano you'd be able to see you're actually hitting the same keys for corresponding notes, for instance, to play C♭, you hit the key for B.
G Major has one sharp, the F♯. This scale goes G, A, B, C, D, E, F♯ and G.
D Major has two sharps, F♯ and C♯. D Major runs D, E, F♯, G, A, B, C♯ and D.
A Major uses an F♯, C♯ and G♯. The notes are A, B, C♯, D, E, F♯, G♯ and A.
E Major uses F♯, C♯, G♯ and D♯. It runs E, F♯, G♯, A, B, C♯, D♯, E.
B Major has five sharps, those used in E Major, plus A♯. B Major goes B, C♯, D♯, E, F♯, G♯, A♯ and B. The C♭ Major scale sounds just like it, but is written to start with C♭instead of B: C♭, D♭, E♭, F♭, G♭, A♭, B♭, C♭. Notice every note is flat.