The Orion is a human spaceflight vehicle developed by NASA following the cancellation of the Constellation Program. It is intended to be used in the return to the Moon, in conjunction with a lunar lander, and for use in a manned Mars mission, as well as the cancelled asteroid redirect mission.
The capsule has full maneuvering capability and plenty of thruster fuel, which allows it to dock even without a service module. Atmospheric entry is relatively easy with this capsule, due to the abundance of fuel. It also has space for 5 Cargo items. By default, it comes with an Oxygen Tank, Battery, and Carbon Dioxide Scrubber. This capsule can be attached to any medium stage. It uses 9 power.
Orion Service Module
The Orion service module is an engine attachment designed for the Orion capsule. Outside of using it to transport Orion, it can be extremely effective as a tug/payload carrier. It has 4/6 fuel capacity, allowing you to reach high speeds, go long distances, or afford mistakes. It doesn't have the risk of running low on power as well.
Orion Multi-purpose Crew Vehicle
To build the full vehicle, you must follow the following assembly:
You can place the vehicle atop any medium or large stage rocket, and have it reach orbit. The vehicle, though, was designed to be launched on the Delta IV or Space Launch System. The Delta IV second stage, though officially a part of the vehicle, runs out of fuel almost as soon as you reach orbital velocity, and therefore is useless. To see the proper way to assemble Delta IV and SLS with Orion, see their respective pages.