Upper stages are typically smaller and lighter than first stages, as they do not need to carry the weight of the entire rocket. They are also more efficient, as they operate in the vacuum of space where there is no air resistance.
Upper stages are often used to inject satellites into orbit. In this case, the upper stage will ignite after the first stage has burned out and will carry the satellite to the desired altitude. The upper stage will then release the satellite, which will continue on its own trajectory.
Upper stages can also be used to send payloads to other celestial bodies. In this case, the upper stage will ignite after the first stage has burned out and will carry the payload towards its destination. The upper stage will then release the payload, which will continue on its own trajectory.
Upper stages are an essential part of rocketry, and they play a vital role in placing payloads into orbit and sending them to other celestial bodies.