What is the spinning circle on IPhone data
Yes it does.  To see how much, or to prevent data access to certain apps when on mobile/cellular visit Settings &gt; Mobile (or Cellular) and scroll to the list of apps at the bottom, here you can see what is enabled for mobile access, and how much data has been used since the last reset point.

You can reset the stats back to zero from the same page any time you like.  This is useful if you know for example that your Data billing cycle starts on the 17th, and you can set yourself a reminder to reset it on that date.

Note that the above is only really useful on iOS7, you don't say what version you use, if you use an older version the same rough idea applies only it's not split by individual applications, and you can't get granular detail or control.