As the name implies, pre-workout is a supplement designed to be taken before you start your workout, for the sake of energy, focus, and a boost to performance.
Pre-workout tends to utilize caffeine as the primary source of energy, so you‘ll find anywhere from 150-300mg per serving. Pre-workout also blends tend to include Beta-alanine (an amino acid), BCAAs, and creatine.
Pre-workout is intended to boost performance during the workout and aid in muscle recovery after the fact. Caffeine, besides providing an energy increase, has been shown to increase athletic performance.