Creatine helps replenish ATP which is the direct chemical fuel for your muscles. By keeping ATP levels high, Creatine is able to provide more energy, endurance and explosiveness which leads to an overall better workout. It is good to have and to mix, but you don't need it. Creatine is only really necessary for serious body builders.
Keep in mind that even the best creatine supplements don't work like magic, there is lots of hard work to be done.