Nearly used all of my data?

I just got a message saying I've used 80% of my data and I don't get any more for another month, what do I do?! I've got an iPhone 5c that I've had for a week, i don't know what data is, I don't know how it gets used up and I don't know how to make my 20% last me another month, especially as I go on holiday next week?!

Turn off data usage under settings for your apps

You need to learn how to manage your data (internet) or bill will be astronomical. Also learn about using Wi-Fi. Basically anything you do on an iPhone that is not a voice call uses data. Start with these links to tips. Best luck.
http://9to5mac.com/...ata-usage/

http://www.macworld.co.uk/how-to/iphone/how-manage-mobile-data-iphone-3488983/

http://www.iphonehacks.com/2014/05/manage-control-cellular-data-usage-iphone.html