As a first step to enable email hosting, add the domain of your organization or business here. After the setup process, you can create professional email addresses for members / employees of your organization in the format username@<your-own-domain> instead of firstname.lastname@example.org
At a later step, you need to verify that you own the domain. For this, you need administrator access to the DNS Management page, where you have registered this domain.
A domain is a unique name used to identify businesses or other entities on the internet. For example, in www.zillumcorp.com, 'zillumcorp' is the domain name. Email addresses of people in this company will have '@zillumcorp.com' at the end instead of @zoho.com or @gmail.com.
Yes, you can have multiple domains configured in Zoho Mail and have email addresses with these different domain names. For example, you can have email@example.com and firstname.lastname@example.org.