Rockets are rocket shaped because of the aerodynamics (the passing of air and other gases around an object) to get the rocket to certain speeds. If it weren't that shape, (say that it was a box...
a multistage rocket is a rocket. a rocket could be a multistage rocket. all multi-stage rockets are rockets, but not all rockets are multi-stage. For example the space misstions. They are all multi...
At the very bottom is the nozzle, after that is the fuel. Depending on how big the rocket is and how much fuel it needs determines the size of the chamber
A solid or liquid propellant is typically oxidized, or burned inside a nozzle. The expansion of the fuel into the gaseous state provides thrust against the nozzle surface.