Liz, if these are torsion springs on the header of the door, then I'm with Jim. Messing with them can cause broken fingers, hands, and parts flying around in your face, etc. Get a pro. If it is a torsion spring, then I could tell you in general what you are facing if you respond with the size of the door and the number of springs above the door and if one or both are broke or what. They are sized like pipe with a certain od and id of the coil, the diameter of the spring metal itself, and the number of twists per foot. If the spring broke in two, then you will have to take it to an overhead door company to get a replacement. Go ahead and have them install it. Money well spent.
The rest of the procedure, I won't go into now until you post back further with more info and info as to who is going to do this, but it requires putting a certain number of twists in the spring according to the weight of the door. Twisting and untwisting is where the unsuspecting get hurt. It is double difficult on a 16' door cause it has two springs that work opposite. It also requires the right tools. An improperly sized rod could slip out or too light of of a rod could break while twisting/untwisting. If one spring of two broke, look for a painted line on the good spring and by counting from one end, you will see the number of twists that were put into it. By the way, removing and installing the spring ends isn't much fun either.