An Apple ID is your online account for Apple's software and services: These credentials are used to download content from iTunes or the App Store; they're also used to log into iCloud, which can help you sync and back up your data, access email, and more.
If you are getting a new Apple ID for anyone over the age of 13, getting set up is very simple. Just open the Settings app and tap Sign in to your iPhone. The process to create an Apple ID will begin after you select Create Apple ID. Remember, you'll need to be able to check the email of the person you're creating the Apple ID for so you can confirm the process. So make sure that's possible before you begin.
If you're concerned with how your little one is going to use their iPhone or iPad, you can set up Parental Controls to restrict the device's usability. You can also sign up for a full monitoring service like Qustodio to keep track of websites, apps, and games your kids are using. Want to put a time limit on their screen time? No problem.
Apple has also added iCloud Family Sharing to the list of shared account options. You'll have to pay a minimum of $2.99 per month for 200 GB of iCloud storage (the minimum for a Family Sharing plan), but it makes it possible for everyone in the family to store their photos, videos, documents, device backups, and more in iCloud where they're safe if something happens to their device.