Using my very rudimentary graphic design/labelling skills I have spent my weekend making this diagram for you, featuring my brand new pelvis, "Paddy" (who lives in Paddington)! She is a female pelvis - obviously the male pelvis is very similar but does not have a vagina. Unfortunately from this angle, you can't see the opening for the urethra but every pelvis does have one, I assure you.
The pelvic floor muscles literally form the floor of your pelvis. They are the last stop between everything inside your body and the outside world, essential for:
Keeping things in when you want to: your pelvic organs (all the time) and urine (when you're exercising or there isn't a toilet close by),
Letting things in: like when using a tampon/menstrual cup or during intercourse, and
Letting things OUT: things like urine and bowel movements at appropriate times, and babies.
Pretty versatile really!