There are several different types of propulsion used today in aerospace. The most common is the solid rocket motor. Nuclear energy can also be used.
Solid rocket motors are made of a few componets. The fuel and the oxidizer make most the motor and do the work. The componets of the propelant are placed inside a casing. On one end is the nozzle and the other is the plug. The motor may or may not have a delay section. This section allow the motor to coast before the recovery system is deployed. The delay may emit smoke as well to visiably see the rockets postion in the sky as it at this point can be very high. Some motors also have a ejection charge that will deloy a recovery system.