among the major things that make the blues the blues are:
~definitive 12, 8, or 16 bar chord patterns
~heavy accents on the I, IV, V chords of the scale (the major chords of the scale)
~the I,IV, V chords are typically played as 7th chords (adding 7th note or replacing 5th with 7th )
~the "blue notes" the pentatonic scale is typically accented with flattened 7th and flattened 3rds (i.e. the note between the 6th and 7th or the note between the 2nd and 3rd).
this is fairly basic list but it addresses the major music theory aspects of the blues.
Musical theory is a lifelong exploration, in order to understand how the Blues style relates to Musical theory you will need to understand the foundations, but it's well worth the effort.