Hammer on : put your fretting finger on a frett and pick, then without picking hammer with another finger on a higher frett.
e.g. put your index finger on the 5th frett on any string, then with your ring finger hammer on 7th frett.
Pull-off : opposite of hammer-on .
e.g. put your ring finger on the 7th frett & your index on the 5th frett of the same string... then pull your ring finger off.
Bend : from it's name , it's bending the string (up or down)
e.g. put your ring finger on the 7th frett , and reinforce it by putting your middle finger on the 6th frett of the same string... and bend up or down (according to the string you're bending)
Normally , the high strings (g b e) should be bent up ... and the low (E A D) strings should be bent down.
If it's your first time to play guitar and you didn't understand what I said , check out Beginners lessons on this site and others.