Want to know how much data you have used well check out the vid posted by our AC, or if you in a hurry just tap the carrier logo on your pulldown shade.
Handy! I setup "mobile data" as one of the quick settings in my main settings menu on my Note 4 just to make it easier to go in to the detailed data usage report. I also have the vzw data widget on one of my homescreens so I can see at a glance where I stand, but this might be a better option if/when it comes to my device.