I need to get the email app

The email app is built in to iOS. While you can remove it, unless you explicitly removed it the mail app is still on your phone. Use Search (put your finger in the middle of the screen and drag down) and search for “mail”. If you see the app it is somewhere on your phone. If it isn’t this Apple support link has instructions to reinstall it ➡️ Remove built-in Apple apps from the Home screen on your iOS 10 device or Apple Watch - Apple Support.

I don’t understand what you mean. Please explain what you mean by needing an email address to get into an app.