Vagina is located in perineal pelvic cavity, in front of rectum and behind bladder. This is a very flexible organ. You can search related pictures online for a more intuitive understanding.

The vaginal orifice is located in the front of anus and the back third of vulva, usually covered by labia minora, and the urethral orifice is located in the front of labia minora. Don't mistake it for a vaginal opening.