How do I wire a light with only two white wires and nothing else?
Strange it came with no documentation.

The backward UR is an underwriters laboratories recognized component marking. It appears to have a C before it and a US after it.
https://en.m.wikipedia.org/wiki/UL_(safety_organization)#Recognized_Component_Mark

That doesn't mean the whole assembly is UL approved but it means that part has been tested.

Either send it back and get a refund, or contact the company that sold it to you for instructions.