There is not much music theory needed to play this style of music, but there are still a few basics that must be understood.
As I mentioned in the previous post, blues is typically played in 5 different keys: A, C, D, E, and G.
Although some blues songs are only played with 1 chord, most are played with 3 chords. To play songs with 3 chords, you will need to learn the I chord, the IV chord, and the V chord.
Below is a handy reference chart which breaks down the I, IV, and V chord based off the key:
Essentially, most blues songs are based around a certain chord. Let’s say it’s an A chord. If we are going to base a song around a certain chord, that means we are playing the song in that key.
Based on the chart above, in order to play a 3 chord song in the key of A, you will also need to learn the D chord and E chord.
If you look at the chart above, you will see you will need to learn to at least one B chord and F chord.
Luckily, nearly every country blues player (and most folk and country players) used a form of the F chord with no barre, and played an easy to fret B7 chord instead of B major.
If you are comfortable with how progressions work, take a look at this post to see diagrams of the chords you’ll need to know.