iCloud - storage and backup

iCloud is Apple's online storage service. It is accessed via the user's Apple ID.  Apple provides 5Gb free storage which can be upgraded. A 200 Gb storage costs $4.50Au a month. This is sufficient to store in the range of 20,000 photos plus other items. PC computers can link to an iCloud account. iCloud backup works in the background and so long as adequate storage is available, provides a thorough safety net of backups.

Sharing
A family can use Family Sharing and have family members with their own Apple ID sharing one account for purchases. Children can be given limited rights to purchase etc. A couple can share one Apple ID and use the same Contacts, Notes, Calendar, iTunes. Apple does not recommend this because it can result in conflicting interests as outlined in the Family Sharing link. But it can work well with a couple, particularly in sharing Photos and Contacts. It is not too good with children who have different privacy needs and interests. A couple sharing one Apple ID can have separate email accounts via Gmail etc.

iCloud is managed in Settings where apps are given access to iCloud online storage.

This is what one's iCloud looks like on the web at icloud.com, but you don't need to go here - all the files are accessed from each of the apps shown.