How do I download my iCloud to new device

If you refer to an iCloud backup when you are activating the new iPhone, start it from a backup. If you refer to everything synced with the iCloud, go to Settings, tap your name (Apple ID) then tap iCloud, tap show all and choose what you want to sync from/with the iCloud

Log in to the new device using your Apple ID that's it.

iCloud is associated with an Apple ID.