The C blues scale has 6 notes: C – E♭ – F – G♭ – G – B♭. The blues scale is the minor pentatonic plus one note, the ♭5 or “blue note”. That note is a passing tone: slide or bend through it and the line sounds instantly bluesy. It works over all three chords of a 12-bar blues.
Compared with the C major scale it has ♭3 (E♭ instead of E), ♭5 (G♭ instead of G), ♭7 (B♭ instead of B).
The explorer above is set to C blues: the whole neck is mapped, and you can zoom into any of its 6 positions, change the labels to degrees or fingers, and hear it up, down and in patterns.