Keeping the genitals clean is important for health.
The doctor performed an examination of the genitalia.
He was arrested for exposing his genitals in the park.
陰部 is a slightly softer, more euphemistic way to refer to the genital area, whereas 性器 is the direct medical term.
Compound of 性 (sei, 'sex, gender') and 器 (ki, 'organ, instrument').