iPad and Iphone clear to dos do not sync

How can I turn on iCloud synchronization between iPhone and iPad, because they do not sync

Sync does indeed seem to be difficult. It was by far the biggest problem of the old Clear. When sync got stuck, there were a bunch of arcane magic tricks you had to perform to unstick it. (Worse, at some point the web page explaining the procedure vanished into thin air.) If it can’t be made more reliable than that, we’re better off without it, IMO.