The Lunar module is made up of two main parts, the Descent and Ascent stages. The Descent stage is the bottom section that contained the large engine, fuel tanks, batteries, supplies and equipment. The upper section was the pressurised crew compartment, and was a spacecraft in its own right, having its own propulsion and manoeuvring thrusters. The two astronauts would fly the two connected sections down to the moons surface, the descent stage large engine being used to control and land the vehicle. When they were ready to leave explosive devices were detonated and the two halves were disconnected from each other and the ascent engine would ignite and hurl them back up into orbit, where they would meet and dock with the command module that had been circling above them. Here is the section devoted to the descent stage build