How do I use my ICloud space to use on my device space

You cannot. iCloud storage is not a substitute for local capacity. It exists on a server only and you can sync content to it from your device, but cannot be used as local storage, not can you move things to it, and not have a local copy on the device,

Its like thinking you have a new room in your house because you rented a storage warehouse at a place like U-Store 5 miles form home. You don't get more space in your house to make an extra room. The space is somewhere else entirely.