How does Facebook, Twitter etc use MB on my iphone?

I would check my usage under settings on my iphone4s. And apps such as Youtube, Twitter, and Facebook would be using MB. I just wanna know what i'm doing that makes it use MB. And how i can decrease the amount. Like when i use twitter, everytime i open it does it use MB? Or everytime i watch a youtube video? Help!

Added (1). Ok so youre saying that everytime i use facebook, open twitter, or watch a youtube video, i'm using data. (Mb, GB on my phone) right?& on my phone it shows the amount available&used under settings<usage right?
**How do i get more storage space on my phone, by doing something about my facebook, twitter, youtube, etc.apps?** is there anyway i can use less data?

In case you didn't know, MB stands for megabytes, and you use megabytes as data usage.

Every app you use, whether you're using Facebook, or even Apple Maps, it uses data when you aren't connected to Wi-Fi.

You know you're using data when there's a circle going round and round next to the 3G symbol on the top black bar on the iPhone.

There's no way to decrease it, as you are using data anyway. In most cases, you'll never use more than you're assigned in your data plan, so it isn't something to worry about.

If you are Really worried about, look into an app called Onavo Extend. It greatly decreases your data usage, without having to do a thing. Download it in the App Store, and follow the on-screen instructions.

Hope I helped!