A hammer on is executed by picking a note and then hammering a left hand finger onto the string. The hammer-on is indicated by a curved line and the symbol H.
This exercise should help you gain control of hammer-ons.
Now try this 8 bar Blues making use of the hammer-on. Take care with the position shift on the Bchord in bar 6.
Here is another interesting shuffle in E, making use of harmony notes.