DESCRIPTION:
Easy guitar lesson from http://hard-guitar.com/ (by Mykola Yermolenko)
How to play Hammer Ons and How to play Pull Offs on guitar Basic Techniques

Step 1 - Pull-Off
Place your finger on the string and pick the string.
Pull your finger down (not bending the string)
so that it plays the open string.

Step 2 - Hammer-On
Pick the open string.
Slam your finger on the string
so that it plays note on this fret.

Step 3 - Hammer-On + Pull-Off
Pick the open string.
And then play Hammer-On and Pull-Off
by turns without a right hand.

Exercises of HammerOn and How to play PullOff