The RS-25 engine consists of various pumps, valves and other components which work together to produce thrust. Fuel comes from the huge external fuel tank burning liquid hydrogen and oxidizer liquid oxygen.
 

This engine uses what's called Turbopumps. There are low speed and high speed turbopumps on the main engine and is the result of many years of refinement. The Low Pressure Oxidizer Turbopump (LPOTP) is an axial-flow pump driven by a six stage turbine powered by liquid oxygen which operates at approximately 5,150 rpm. It boosts the liquid oxygen's pressure from 100 to 420 psi.
 

The High Pressure Oxidizer Turbopump (HPOTP) consists of two single stage centrifugal pumps (a main pump and a preburner pump) mounted on a common shaft and driven by a two stage, hot gas turbine. The main pump boosts the liquid oxygen's pressure from 420 to 4,400 psi while operating at approximately 28,120 rpm, giving a power output of 23,260 hp. The temperature in the combustion chamber reaches 6,000 °F, higher than the boiling point of iron.
 

You can see a some of the many thrusters that are located on both sides in the rear and at the nose. They all use the same solid propellant as the OMS does.
 

This shot gives you a good look at all the tiles along with the leading edge of the wing which was damaged on Columbia by falling debris during launch, causing it's burn up on re-entry in 2003. The yellow framework holding the shuttle uses the same three mounting points as when it's being carried by a 747.
 

You can see three of the four large cargo bay doors along with the American flag pointing in the right direction. You can also see the pod which stores the solid propellant for the OMS engines and thrusters.
 

The yellow arrow says 'rescue' inside of it and is pointing to the rescue hatch. This was added to Endeavour which the space shuttle Columbia didn't have, not that it would've helped them.
 

The main power sources of a space shuttle are the fuel cells (F/Cs), which combine hydrogen and oxygen into water and derive electricity from this process. Most of the water is used internally in the spacecraft (either as coolant or used by the astronauts), but to avoid degradation of the efficiency of the fuel cells, excess water is purged from the cells into space through this port (top yellow tag) and another like it on the other side. The bottom tag says, "to remain clear and open at all times".