Q: I AM VERY CONFUSED about using the icloud. My mini pad has used 13.1 GB and only 388 MB available. I need to apply the iOS 8 update. But I don't have enough space. I have 20 GB in my cloud and only 3.5 GB has been used. Why isn't the data being sent

The space on your device is not really related to the space you have on iCloud servers. iCloud is used for backup & syncing a few file, the data still needs to exist on your device.

If you want to update the device I suggest you connect it to iTunes on your Mac or PC. That will allow the update to happen without requiring too much space on the device. Use the computer that you have previously used.

If you must install only using the iPad (an 'over the air' update) you will have to delete some files to have enough space for the update - iOS needs to download the update & then it can be installed.

These may help you to see where your storage is being used…

See how much storage you've used on your iPhone, iPad, and iPod touch - Apple Support

Delete music, movies, podcasts, and other content from your iPhone, iPad, iPod touch - Apple Support