Blues is a unique form of jazz that has consolidated since the year 1900 as a cyclical harmonic progression with three basic chords: I7-IV7-V7, a structure of 12 compasses and three AAB sentences .
In a rhythmic way, the accompaniment is uniform, However, the melodic line is irregular, blues is often improvised.
In the melodic field it uses the blues scale and the “blue notes”, (b3 and b7).
I7 | I7 | I7 | I7 |
IV7 | IV7 | I7 | I7 |
V7 | IV7 | I7 | I7 |
I7 | IV7 | I7 | I7 |
IV7 | IV7 | I7 | I7 |
V7 | IV7 | I7 | V7 |
I-7 | I-7 | I-7 | I-7 |
IV-7 | IV-7 | I-7 | I-7 |
bVI-7 | V7 | I-7 | V7 |
Like I said, this is just a guide, (what we work in class in James Rae's book is the first example, the most archaic), nowadays composers have been adding harmonic progressions to make it richer in the harmonious field.

This is the blues scale, but if you want to learn how it is built and used, watch the following videos.
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