There are some other pinned threads in the girl's resource center about periods, and this one includes some facts that aren't covered in those threads.

More about Periods Q&A

Q: My mom starts her period at 15, does that mean I will start my period at 15 too?
A: That is very likely to happen, genetic factors do affect your menstruation.

Q: How do I know when my first period is coming?
A: Puberty signs including breasts formation, pubic and armpit hairs, also the white discharge from your vagina.

Q: What if I never get my period (age 16 w/o menstruating)?
A: You might have amenorrhea, so consult the doctor about it.

Q: When will I stop having my period?
A: Menopause, around ages 45-50.

Q: How does menstruation feel like?
A: Just dampness in your crotch and underwear.

Q: Ahh! Menstrual odor!
A: Use tampons or changing pads frequently will reduce or take care of the problem.

Q: Does having your period hurt?
A: No. But cramps might happen. Take midol (or other pain relievers) if cramps happen.

Q: Do people/boys know that I am on my period?
A: No, unless you tell them.

Q: Do boys menstruate?
A: Boys have different reproductive systems than girls, so they don't have their periods.

Q:Pads or tampons?
A:
Pads are user-friendly to starters, and they have different sizes, which depend on your menstrual flow and your body shape.
Tampons are good for swimming and when you don't want pads to show through your clothes, however, getting started with tampons might be uncomfortable, but you will get used to tampons later on.
Pantiliners are good for backup for tampons and light flow days.

Q: How do I tell Mom that I got my period?
A:
Choice 1- Just tell her, and be comfortable about it.
Choice 2- Write it down and let her read it.
Choice 3- Open up a conversation with her and come up with a topic about periods.

Q: But I only live with my Dad!
A:
Choice 1- Talk to someone he trusts, probably a female friend or relative of his, because it is more comfortable to talk to a woman about it.
Choice 2- Ask him to make you a doctor's appointment. You can leave the decision to the doctor if you don't want your dad to interfere with that.
Choice 3- Just tell him, and be casual, keep it simple and brief.

EDIT:

Q: OMG, my period hasn't come for [insert number here] months!
A: It's normal to have irregular periods. So get over it.

Q: Why is my period blood brown?
A: It's because the blood is dry and it's perfectly normal.

Q: Grr, what's that white stuff in my underwear?
A: Vaginal discharge is very common among girls, just wear a pantiliner and stay dry and fresh.

Q: How to prevent leaks for irregular flows?
A: Change pads/tampons often, or use a high absorbancy pad. Or tell your mom about it, she might be able to help you.

Q: Why are there chunks of blood in my period?
A: Those are clots from the uterine tissue. Again, it's normal.

Q: Is it safe to use scented tampons?
A: Yes. If you are worried, use the unscented ones.

Q: How can I prevent leaks during sleeping?
A: Use pads if you sleep for more than 8 hours, since most tampons should be changed every 4-8 hours to prevent TSS.

Q: Can I swin with a pad?
A: No, you have to use tampons.

Q: What if I started my period in some places without pads (ie. in the school bus)?
A: Use toilet paper and roll it to make a temporary pad.

Q: Can I shower during my period?
A: Yes, and you need to be more careful too because dry blood can cause irritations.

Q: How do I hide an unexpected leak?
A: Bring extra panties and jeans and keep them in your locker. Put extra pads/tampons there too.

Researched about periods in beinggirl.com and I wrote those Q&As myself.

If anyone has anything added to it, feel free to add it with replies. If you think this topic is helpful, feel free to add this topic to the girl's resources center.

you should also have questions about irregular periods...and the colors...

Thanks for the suggestion, I have edited the post with more Q&As.