The display should have come with a 12V adapter. The adapter allows you to use the regular 2.1mm barrel jack:
The display is very easy to use - simply connect the included 12VDC adapter to the 2.1mm center-positive DC jack, then connect a composite video source to one of the RCA cable.
If you did not receive the 12V adapter, please contact email@example.com
for a replacement. Reference this thread and your order number.