How do I move all my ipad photos to icloud? .

You turn iCloud Photo Library on in Settings > iCloud > Photos. However it doesn't "empty" the pictures to the cloud. The most you can do to free up space using iCloud is to turn on Optimize Storage to keep a smaller device-sized version of the photos on your iPad. See the quote below from iCloud Photo Library FAQ - Apple Support

Can I use iCloud Photo Library to save space on my device?

iCloud Photo Library automatically keeps all your photos and videos in the original, high-resolution version. Follow these steps to choose how you store your photos and videos on your device:

• In iOS, tap Settings > iCloud > Photos or Settings > Photos & Camera, then select a storage setting.
• In OS X, click Photos > Preferences > iCloud, then select a storage setting.

If you turn on Optimize [device] Storage, iCloud Photo Library will automatically manage the size of your library on your device, so you can make the most of your device's storage and access more photos than ever. All of your original, full-resolution photos and videos are stored in iCloud while device-size versions are kept on your device. You can download the original photos and videos over Wi-Fi or cellular when you need them.

If you turn on Download Originals, iCloud Photo Library will keep your original, full-resolution photos and videos in iCloud and on your device. Download Originals is the default setting for iOS devices with the free 5 GB storage plan and for all Mac devices.

It's hard to tell what you have done and what you are trying to do as you originally asked about moving photos to iCloud and then deleting them from your iPad and your second post is talking about backup.

1: A backup to iCloud is one thing. For that you go to Settings > iCloud > Backup and turn back up on; that will allow automatic backups when you are connected to wi-fi, have the device plugged in to electrical power and the screen is locked, You can also manually trigger a backup by tapping the "Back Up Now" on that same screen. However a backup to iCloud can only be used when doing a full restore; you cannot log in and see the contents of the backup. You can go to Settings > iCloud > Storage > Manage Storage to see how much space the storage is occupying on iCloud. More information on iCloud backup: How to back up your devices using iCloud or iTunes - Apple Support

2: A completely different thing is iCloud Photo Library which will allow you to see the photos when logging in to iCloud. There are instructions about how to turn that on in my post above. The optimize storage option is in Settings > iCloud > Photos. See the link I gave in my first post for more information on iCloud Photo Library.