An AWS root user is created whenever someone creates an AWS account. When creating an AWS account, we provide our email as the login name. When the account is created and you log in using your email, it means that you are using your root account. The root account credentials are the email ID that you use to log in and the password. 

The root account has the maximum permissions. In fact, you have unrestricted access to all AWS services when you use the root account. The root account has access to all of the billing information and credit card and debit card details. You can add more credit cards and debit cards to the account, modify the payment methods, and so on, using the root account. You can also change your password using this account.

The best practice, as suggested by AWS, is to use this root account to create other users, with an admin user among them. This admin user can then be used for day-to-day activities. AWS suggests that you do not use the root account for day-to-day activities. It goes without saying that since the root account is a very powerful account and provides access to all of the resources, the credentials of the root account must not be shared with anyone.