There is a lot of talk about the vagina and vulva these days, and while these terms are often used interchangeably they are actually two different parts...that are treated differently in terms of hygiene and even hormones.
Starting on the outside of our female bodies is the vulva, derived from Latin for wrapper or covering. The vulva is considered the external female genitals and includes the mons pubis, labia majora, labia minora (pronounced just like the candles), clitoris, urethra, and opening of the vagina with all its glands (Skene's glands and Bartholin's glands). (Note: does not include the vagina).
The mons pubis is the tissue covering our pubic bone (lovingly referred to by some as FUPA (Fat Upper Pubic/Pu**y Area). This fat cushions the area during intercourse, otherwise the people who love to refer to it as FUPA would be jabbed by our pubic bone. The labia majora and minora are the large (outer) and small (inner) skin folds, respectively, that cover everything up down there. These are often called the lips. The labia majora and minors are the embryologic equivalent of the male scrotum and penis shaft, respectively.
The clitoris is the organ that most women get the greatest amount of sexual pleasure from. The clitoris is analogous to the head of the male penis and even has a cute little covering of its own called the clitoral hood (equivalent to a man's foreskin). When a woman is aroused the clitoris engorges and pushes the hood back. The function of the clitoris is purely sensory with over 10,000 nerve endings...no more explanation needed.
The urethral meatus is the opening where the urine comes from and sits right below the clitoris at the top of the vaginal opening. This is one of the three holes women have: urethra, vagina, anus.
While all of the above are considered part of the vulva, the vagina itself is not. The vagina is the muscular tube that connects the vaginal opening to the cervix (opening to the uterus) and its main functions are intercourse and childbirth. The upper part of the vagina also does not have a male equivalent part.
So what does this mean in terms of how you care for your vulva and vagina? In general, since the vulva is external it can be cared for the same way you would other parts of your body (but maybe a little gentler). If you have sensitive skin, chances are the skin of the vulva will be sensitive so you should use washes and moisturizers suitable for sensitive skin. On the other hand, the vagina is its own little ecosystem and is a self-cleaning oven so washing internally (douching) is discouraged. As far as hormones, the vulva can respond to both estrogen and testosterone (remember the vulva has equivalent male parts) while generally the vagina responds best to estrogen.
Take home message: your vulva and vagina are different parts.