The biceps brachii are two sets of muscles in the upper arm of human beings. There are two branches or "heads" of the muscle that are attached to the scapula. From there, the branches converge into a single large pair of muscles and the muscles runs from the shoulder to the elbow.
Although the primary purposes of the biceps is to draw the forearm towards the upper arm, the structure of the biceps gives it a large range of functions, such as applying a twisting motion with the hand and applying a force towards the shoulder typical of pulling. As such, although it is capable of applying a large amount of force (such as lifting a dumbell), it is also capable of delicate movements as well (such as using a screwdriver).