T' propellant in composite solid rocket motors consists o' a fuel and oxidizer which are separate, but mixed together. This contrasts with motors, such as black powder model rocket motors, in which t' propellant is made up o' a substance ontainin' oxygen and fuel in t' same compound.
T' video below illustrates t' assembly and function o' a typical composite propellant (APCP) rocket motor as used in many hobby rockets.