How does a UV LCD 3D resin printer work?
I'm surprised your research hasn't answered your question, as the concept is relatively simple. You have most of the answer in the question. The missing item is a light source. Usually the source is an array of ultraviolet LED modules. There are resin printers that would not be called LCD printers, as they use computer display projectors to generate both the image and the UV to cure the resin.

A rather extensive list of various resin printers can be found at aniwaa.com along with a clear explanation of the technologies.

The image below is courtesy of the link in the previous paragraph.



The light source that answers your question is visible in the third picture. As noted, the LCD panel blocks the light based on the image to be cured. I think the "uses its own light" is somewhat misleading, unless the builder has found a high-UV output LED LCD panel or is using daylight resins and has configured for long burn-in times.