When you set up iCloud, you automatically get 5GB of storage. You can use that space for your iCloud backups, to keep your photos and videos stored in iCloud Photos, to keep your documents up to date in iCloud Drive, and more.
Sign out of iCloud on your iPhone, iPad, iPod touch, Apple TV, or Mac
If you want to stop using iCloud on one of your devices, learn how to sign out and what happens when you sign out.