How rockets work?

Soyuz Rocket
This Russian Soyuz [[KW]] rocket [[/KW]] carried cosmonauts to the Mir [[KW]] space station [[/KW]] in 1992. The boosters attached to the outside of the first (bottom) stage of the rocket are clearly visible in this photograph.
Novosti Press Agency/Science Source/Photo Researchers, Inc.

Rockets are very powerful, but it is often more efficient to use several rockets, rather than a single rocket, to move an object to the desired place. Launch vehicles often use more than one rocket engine, or stage, during a mission. In [[KW]] rockets [[/KW]] that use stages, the stages are stacked on top of each other. The stage on the bottom of the stack is the first one to fire. In some rockets that use stages, the first stage has additional rockets attached to the outside, acting as boosters to further increase the thrust. Rockets can theoretically use any number of stages, but the complications caused by coordinating the firing times of the stages make it impractical to have too many. The huge Saturn V rocket that sent Apollo astronauts to the Moon had four stages, including the Apollo spacecraft’s own rocket.
The first and most powerful stage lifts the launch vehicle into the upper atmosphere. The first stage then separates from the rest of the rocket and falls toward Earth. Some first stages, such as the space shuttle’s booster rockets, can be recovered. Others, such as the first stage of the huge Saturn V Moon rocket, burn up in the atmosphere once their fuel is expelled and they drop off the launch vehicle.
The second stage carries less weight than the first stage, because the first stage has dropped off of the rocket. When the second stage takes over, the vehicle reaches a much higher speed; the second stage, however, also uses up its fuel and drops off. The third stage fires and places the spacecraft into orbit (for a mission designed to orbit Earth). On deep space missions, the third stage allows the spacecraft to reach escape velocity and head away from Earth. For some missions, three stages are not adequate.
Engineers can reduce the number of stages a launch vehicle needs by getting a rocket closer to its destination through some other means. For example, an airplane carries the Pegasus rocket, which sends spacecraft into space, to a high altitude first. The rocket then fires and carries its cargo into orbit.