This is a polite way of saying that he has sexual relations with his father's wife. Some languages use more direct phrases such as "has sex with his father's wife." (See: [[rc://en/ta/man/jit/figs-euphemism]])
Here the idiom “uncovers … nakedness” means “disgraces.” See how you translated this idiom in [Leviticus 18:7](../18/07.md). Alternate translation: “he disgraces his father” or “he shames his father” (See: [[rc://en/ta/man/jit/figs-idiom]])