Guitar Scales for the Blues
Choose a root and a type. Most players start from the minor pentatonic and the blues scale; the rest are a click away.
Choose a root and one of 24 types to see it laid out on this seat's fretboard, roots marked throughout.
On the guitar a scale is mostly raw material for bends: a note a fret or two below the one you want, pushed up until it sounds right against the chord, which is how a fretted instrument reaches the pitches between its frets.
Whatever scale you start from, the blues bends it: the third and the seventh get pushed flat, or somewhere between flat and natural, and that pull against the chord underneath is most of what the idiom sounds like.