how do you move ipad storage to icloud storage

You cannot do so. They are physically separate things. iCloud is essentially a service to synchronize data across your devices. It is not archival storage nor is it an extension of your device storage.

If you turn on iCloud photos in your iCloud account settings, your photos will sync to iCloud. They remain on the device as well though and if you delete one on the device it will be deleted in iCloud. That is because iCloud exists to sync that data to your devices, not store it independently.

See -> Set up and use iCloud Photos - Apple Support