What happened to my storage??

okay so I got my phone like an hour ago, and I go on the App Store to get Facebook, Snapchat and Instagram and it won't download. I press on get and then install and it doesn't do anything. So I went onto my storage settings and I only had 100mb!! I don't know where it has gone as I have no photos on it and no applications. As a test I downloaded a game and it worked however it wouldn't work with the social media. I have since uninstalled the game though and it is still at 100mb. I'm confused??