What is it?

I got my period today and there is this black looking stuff in it like chuncks of something what is that? it is gooey too. what is your period made of anyway?

The blood that you lose when you have your period is blood that your body is getting rid of. The chunks in the blood are called clots. Most women have them but most of the times they fall right into the toilet and you don't notice them at all. There's nothing wrong with you if you are producing clots. Everything is perfectly fine so don't worry! Good Luck!

Sorry but I have to correct you a little bit, chynawhite.

Menstruation (your period) happens when the lining of your uterus (called the 'uterine lining') sheds. The uterine lining builds up and thickens when you are fertile, preparing your egg to be fertilized by a sperm cell. If it hasn't been fertilized, then the egg, uterine lining and blood from the lining will leave your body through your vagina in the form of your period.

So, the 'chunks' and 'gooey stuff' you are talking about is your uterine lining, although some of it may be blood clots. The 'black stuff' is just old blood. Blood becomes black/brown when it's in a clot/dried.

Your body just doesn't get rid of blood like chynawhite said. The uterine lining is part of your body, so when it breaks down (into chunks) during your period, of course there will be blood from it.

For more information, check out these websites:
http://en.wikipedia.org/wiki/Menstruation
http://kidshealth.org/teen/sexual_health/girls/menstruation.html

The blood you are losing is the blood from the uterine that lined it preparing for pregnancy. When no fertilized egg implanted itself in the uterine wall the blood flows into the cervix and out the vagina, and this your period.
Periods normally have clots, but on occasion they do occur. Normally, passing clots is nothing to worry about. If you are bleeding way more than usual, having periods closer together and bleeding heavily and passing a large amt of large clots, and feeling overly tired on a regular basis, and your skin is pale you should contact your Dr as you might be anemic. As always, if you are sexually active see your gynecologist regularly.