The vagina is tubular (tube like structure like a hose pipe). It has an elastic wall that allows the cavity to strech very wide and than to shrink back to its original size. It streches wide enough to allow the passage of a baby during child birth.
It streches from the external ( outside ) opening of the female genital tract towards the womb. The neck and mouth (cervix) of the womb bulges into the the upper part of the vagina.
The vagina accomodates the the male penis during sexual intercourse. The male sperm cells (seed cells) are deposit in the upper part of the vagina.