The transition from progression 1 to progression 2 is a simple one. It's more usual to play minor 7th chords instead of straight minor chords when playing a blues in this way. This is much the same as with a major blues where we'll play dominant 7th chords in place of normal major chords. It gives us a more 'bluesy' quality.
Here, again, we're using basic open string versions of each chord to get used to where we can change chords without worrying about complex shapes to get our fingers around.