In order to create a new e-mail account on your domain you have to start by logging in to your cPanel.
If you are unsure about how to login to cPanel check this link
When you've logged in, find the "Email" section and press "Email accounts"
When you add a new account, you only need to type in the actual name of the e-mail adress.
The "@" and domain will be automatically filled in by the system, you can also choose to create e-mail accounts on more than 1 domain under the "Domain" list.
And then just press "Create account" and you new account is created.