To create email accounts for your addon/subdomain accounts you’ll need to use your cPanel account to first create the appropriate addon/subdomains. Once setup head to Home > Email > Email Accounts.
There you can create the email account for the appropriate subdomain. Be sure to choose the appropriate addon/subdomain from the dropdown menu.
For additional guides on setup:
What is the difference between email in addon/subdomains and regular domains?
There is no difference between the two, as they all create a unique email address that you can send to. The difference only comes from what the name looks like after the @ symbol.