Your iCloud storage is the info from your device that gets saved with Apple in the Cloud - it's an external drive not on your device, similar to Google Drive. If your iCloud storage is full, you won't be able to save/backup your information in case of an accident (device stops working or you crack your screen and it won't work) so we can use it on a new iPad - you will lose everything that didn't backup. It's important to make sure you keep your storage controlled so you'll always have the most current backup available to you and not lose all of your work.

Below you'll find how to fix this and help your iPad to function properly.