I will explain using example of Hostinger.
Suppose you have got a domain and a hosting platform through Hostinger. Your domain registration has been done by Hostinger. In case you want to know the details of your Domain registrar you can visit this link.
Go to lookup.icann.org. In the search field, enter your domain name and click Lookup.In the results page, scroll down to Registrar Information.
You can create a non-gmail email in the form XXXX@domainname.com. For example I have this email id: ariana@unboundedland.com
This can be done through domain management option in Hostinger. Simply log in to hpanel and set up your email.
Once, you have completed the set up, you can access your email through webmail. For hostinger hosted websites this can be found at below link:
I hope this helps!
If you need any help in accessing your domain specific emails in a fast and smooth manner, comment below. I will be happy to help.