What's uses data, and how can I manage it? (Verizon)?

My family and I are going to be getting the iPhone 5's with 4gb of data a month. I would like to get more, but we I don't think we can afford it. There's going to be 4 of us with iPhones and I saw that the average user uses 1-2gb a month. So we may be coming in close of our limit. My question is what uses up data and how can I manage it so we don't use up alot? Also if I'm connected to Wi-Fi, then will my data be used up? Thanks in advance.

Added (1). Also let's say I'm in my house and I'm connected to Wi-Fi and a cell tower and I'm using the internet, since I'm connected to Wi-Fi will it use my data?

Wi-Fi is free, data is only through cell tower. If you don't watch video online then you also won't use that much, I use only a few hundred meg a month but never watch video.

Go to the Verizon website and find the data calculator. This will show you how much data you use with your smart phone.

  • When does data for a iphone from Verizon reset? And what uses up data? I just got an iPhone and I'm getting messages that say that the "usage reset date" is 10/10. Does that mean that is the day my data will be reset? Also, what uses up data? All I've been doing since I got my iPhone is texting and looking at a few things on the internet but I'm always connected to my Wi-Fi.
  • What uses data on an iPhone? So I just got my iPhone, and I have a 1GB Family Share Plan with my dad. He said to be careful about going over the data limit, or Verizon would end up charging us extra… So what uses up the data on the phone? I know that if I'm connected to wi-fi it won't be affected, but if I go on Safari or YouTube using 4G, how much will it take? Can someone tell me what exactly effects the phone's data usage?
  • What uses data for my iPhone 4s? I have three questions: When I'm connected to Wi-Fi and I go on apps and stuff does that use data? So what uses data on the iPhone 4s? What is the cost if I go over my data limit?
  • My iPhone can't use data uses connected to Wi-Fi. Why is this happening? I don't pay for the bill or anything like that, so is it possible my grandfather resricted data to Wi-Fi?