The vulva is the external parts of the vagina, and the vulva is important for both sex and birth.
While many words have many meanings, vulva is not one of those words. The only thing this word refers to is the external (outside) parts of the vagina. This includes the labia, the opening of the urethra, and the clitoris, which is the female sexual organ. You can think of the vulva as the opening to the vagina, but it is also very important in itself.