How much gigbytes do i have left on my iphone 5? (internet)?

I'm having trouble keeping tracks with how many times i can use the internet on my iphone5 before the bandwidth is gone. I go to about and my capacity is 13.3 and available is 12.6. Then i went to my usage and at first the number on the very top right corner was at 20.6, then it dropped to 19.6, then it went up to 19.9. My website data is 18.5. Can someone help me understand how many gigabytes i have left for the internet. What happens when i lose it all up? Do i wait for a month before it is restored again or wait until my parents pay the bill? What is streaming? Does it mean if you open up one site and that's that? Or is it when you open a website and type in all these topics in the search bar?

Check with your provider for exactly how much you have used.

The amount renews every month, when you use it all up you get more the next month.