Once you've registered a domain name and created a mailbox, you can set up your email in your preferred client. This article explains how to set up your email in the iOS Mail application for your iPad or iPhone.
Go here to get started.
Enter your email address and tap on Continue.
On the email setup page, you can choose to view instructions for iPhone/iPad or MacOS (the former should be selected by default). Follow the steps on this page to set up your email.
✔ Tip: Find out how to set up your mailbox in other email clients.