How does data usage work on cell?

I just recently got a new plan, since I got a new phone. My mom, put a plan with me my brother and her on it with sprint, after about two weeks of having it, she warns me, we only have 5gb (it might be mb, i'm not sure) of data. And to not use it all cause she doesn't want the bill to get too high, and all that. But I use the internet A LOT, and I thought we had unlimited! Is their anyway to check? I have an iphone if that helps any. And like say I'm using wi-fi and get on like Pandora or something, it doesn't count as data right? Or like what if I download twitter, but I'm not using it right this moment, is it still taking up data? I have NO idea how this works! I'm use to unlimited, please help!

OMG i have the same problem well had, you can't really check it unless you call you can go to your settings and click phone and read the diffrent stuff they have. I really hate when that happens to me though but you can't go on the internet unless your connected to your home Wi-Fi because if you go on it without it being connected your bill will go up and you will have to pay $20 more.

1. Go to settings
2. General
3. Usage
4. Scroll down to cellular usage
5.In the cellular data network category it will say how much was sent and how much was received, add those two numbers together and it will give you the total amount of data that you have used on your phone in total (does not reset each month)