The biceps are located on the upper arm. The muscle actually crosses both the radio-ulna, elbow and shoulder joints -- but most of its function is to do with the elbow and radio-ulna when it flexes the arm and supinates the forearm.
There are 3 muscles to the biceps:
1. Brachialis - flexes the forearm while the arm is in supination
2. Brachioradialis - flexes the arm when the it is pronated (palm facing the ground)
3. Biceps brachii - supinates the forearm (turns the palm up) and flexes the arm while it is supinated.
These 3 all happen at the elbow and radio-ulna joint; but the bicep also has a function at the shoulder joint where it assists with stabilization of the shoulder.
1. Weak flexion (arm forwards and up)
2. Weak abduction (arm out to side when it is externally rotated)
3. Weak horizontal adduction (arm across the body when it is medially rotated).
Biceps are used quite a bit in a back workout - All Chin-ups, Pull downs and Rows will use your biceps. That's why it's good to think big and then small in your workouts! Train your big muscles first (like your back/chest) so that you get the most out of them... and then train your little ones (like your biceps and triceps).