Answer:
A half life is the amount of time it takes for there to be half of your original amount.
5730 years is the half life for carbon 14 (it's not important to your question. But it does help understand it more).
So, if you start with 1000 grams. After 5730 years, you will only have half of that.
Then after 5730 more years, you will have half of the halved amount. Do you see the pattern?
Hope this helps.