I'm curious how you would know what implantation bleeding is.....
Regardless, yes, it's your signal that you will soon have a period, so be sure you are prepared. You could be lucky and you could have regular periods right off the bat. However, there are many girls that have irregular periods. If you are one of these girls, be sure you are tracking when your period starts and stops so you can try and find a pattern. If you are young and have irregular periods, it usually straightens itself out in your twenties.
If you have irregular periods and you are silly enough to have unprotected sex, it will be hard to tell if you are pregnant. So don't engage in sexual activity unless both of you are using birth control.
During your period, you may experience bloating and cramps. Midol or Pamprin usually helps with this. You may feel *itchy - that's normal. Try not to bite someone's head off, however. Just realize that it may happen and try to zip your lip if you're feeling sassy. Welcome to womanhood!