Of course, you'll also need a set of jumper cables. Note that the jumper cables feature color-coded clamps at each end. Red is for positive terminals and black is for negative and ground. A basic set of jumpers should run about $20 and is a must-have for every driver's roadside safety kit.
Make sure both vehicles are parked with their engines stopped. Pop the hood of the live car and connect the jumper cables, starting with the red connection to the positive battery terminal. Usually this will also be marked with a red cap. If not, look for a "+" mark.
Do not connect the black clamp to the dead battery's negative terminal. Instead, connect it to a grounding point on the engine block or the vehicle's chassis. There's usually an easily accessible tab on the front of the engine block that works great for this purpose.
Fire up the engine of the healthy car, let it run for about 30-60 seconds, and then attempt to start the disabled vehicle's engine. If it turns over, remove the jumper cable connections, starting with the engine block ground. If not, you may have a bigger problem than a simple discharged battery.