Step 1- Decide where in the car the system is going.
Practically speaking, mobile video can be divided between front-seat and back-seat systems.

Front-Seat Systems- They consist primarily of in-dash receivers with monitors. These receivers fit in a standard DIN-sized opening, and usually have a monitor that's motorized and retracts into the receiver's chassis for storage.

Back-Seat Systems- They usually involve monitors that can be installed in various locations, such as in the headrests, on the ceiling, separate DVD players, and audio components (such as wireless headphones).

Step 2- Choose the accessories you want.
You can add a TV tuner or video game system in a multi zone system, where you can watch one thing up front and hear that sound through the car's speakers while the passengers in the back seat are watching something else and listening to it on wirelss headphones.

Navigation- You can also add on a navigation system that can be used on the front monitor while movies are playing on the back-seat monitors.