AirDrop sharing what is it

I have a iPhone 6 Plus I am trying to figure out why am you so much data using so much data there are five people in our plan and I am using Waymore than any of them not doing anything more on it then I was doing a year ago and I'm trying to figure out what different things mean on this phone like airdrop sharing I don't know what that means I compared my phone with my friend .she would be then when I share this account with and we were just trying to make sure I had right things turned on ring wrong whatever everything off I need help please