This exercise is from the Core Skills exercises on string Bends.

Here we play a simple 12 bar blues tune, using quarter note bends. Quarter note bends are bends that effectively go up by only half a note. Half bends are bends that go up by 1 full note, and Full bends are bends that go up by 2 notes.

Half and Full bends can be difficult to play down at this low neck position. However, quarter note bends are easy enough, and their 'off-note' sound really suits the blues style.

Each bend is played with the 2nd finger. Bend downwards, towards the floor or you will pull the string off the fretboard. Also, while you bend, mute the adjacent string. This will likely happen quite naturally anyway, because as you bend downwards it is likely that your 2nd finger will mute the adjacent string as you pull the string down.

The 12 bar blues progression is in E minor. It cycles through this format:

E riff (*4) - A riff (*2) - E riff (*2) - B5 (*1) - A5 (*1) - E riff (*1) - Turnaround riff (*1)

Each number is a bar. If you add up all the numbers you get 12 (hence the name 12 bar). To learn more about 12 Bar Blues construction, go here.