The muslces of your triceps work to straighten your arm. They work antagonistically with your biceps muscles. Triceps primarily help your pectoral muscles with pushing activies.
Try some of the following exercises:
Close Grip Push Up: http://www.exrx.net/WeightExercises/Triceps/BWCloseGripPushup.html
Cable Tricpes Ext. w/ Rope: http://www.exrx.net/WeightExercises/Triceps/CBBentoverTriExtRope.html
Triceps Kickback: http://exrx.net/WeightExercises/Triceps/DBKickback.html
Skullcrusher: http://www.exrx.net/WeightExercises/Triceps/BBLyingTriExtSC.html
