Chinups allow you to work your lats in the same plane as your bench press. Some lifters feel training them in the same plane works the lats in a way that is most beneficial to their bench press.
With a bar set up in a power rack and your feet up on a bench, pull yourself up so that the bar contacts your body at the same point you lower your bench press to. Your body should be horizontal in the top position. A bench grip can be used as well as wider or narrower grips. A reverse grip can also be used for variety. Plates can be placed on the body or bands can be strung under the base of the power rack and over your body to add resistance.
Some people find they are unable to touch their chest to the bar, this is due to weak lats and will improve with practice. Doing pauses for up to 10 sec. with your chest touching the bar is another way to add intensity to the movement