Most blues songs consist of a 12 bar pattern. If I were to relate this to piano, I could explain it through chord progressions.
For the first four bars of the 12 bar blues, there would simply be a I chord.
For the second 4 bars of the 12 bar blues, I would use two IV chords, and 2 I chords.
For the third 4 bars of the 12 bar blues, I would go to a V chord, a IV chord, a I chord, and back to a V or I chord.
If I were to do this in the Key of C, my I chord would be a C chord, my IV chord would be a F chord, and my V chord would be a G chord