Whether you want a website, custom email address, or both with your domain, it all begins with registering your domain name. There's only one kind of domain name you can register, which you would use for email, websites, or both.
When you register a domain name, what you register is called the root or naked domain, e.g. iwmn.com. Some services require you to set up your domain with the "www" prefix: www.iwmn.com. That's fine, and is just part of the DNS records setup. You do not register the domain with "www" in it.
The root domain is also what you use to create custom email addresses. When you set up your email hosting, you create usernames to complete the email address. E.g. if you wanted a general email address for your company, you might use info as the username, so the email address would be firstname.lastname@example.org.
Or if you are setting up a personal account, you could use your name and create something like email@example.com or firstname.lastname@example.org.
When setting up email, you set up nameservers or DNS records to connect the domain name to the email hosting provider in your iwantmyname dashboard. You create the actual email addresses in your account with your email hosting provider.
To offer a broader range of options and services, we have a variety of email hosting provider partners. You can see the full list in our Marketplace.
Many people are just looking for a simple custom email option and one or two addresses. There are quite reasonable subscription tiers from many hosting providers, though Zoho Mail is the only one that still offers a free plan that works with a custom domain. However, they have significantly limited the features, so be sure to read up on what's included to make sure it would meet your needs.