when i try to download fb it tells me that the item is over 100 mb and it never downloads

If you can't get a WiFi connection, you can use iTunes on a computer to download, then sync, the app.

https://support.apple.com/kb/PH19460

Mscarter13 wrote:

What does this mean

You cannot download apps over 100MB while on cellular. You will have to use wi-fi, as it indicates in the message you see on the screen.