Great, clear explanation, Kathy.  Joanna doesn't say how old she is, but I think this explanation can be simplified by her mom, if necessary, without leaving anything out.   

I would add one thing more.  Joanna -- breasts are not a sexual organ/gland.
They are a modified sweat gland.  Not only do both men and women have usually two, sometimes they might have extras.  These are most often found along the same line, top to bottom, as the "usual" pair, and  are sometimes found into the armpits.  They are called supernumerary nipples.  In some moms who are breastfeeding, they may even initially produce colostrum and milk.  If they are not used to feed, the supply cuts back in those nipples, while the main pair continues to provide food for the baby.

Sincerely, Chanita