To create and manage your email account log into your client area.
Then click your active service.

A subdomain is a subsection of your website that can exist as a new website without a new domain name. Use subdomains to create memorable URLs for different content areas of your site. For example, you can create a subdomain for your blog that is accessible through blog.example.com and www.example.com/blog.
After creating the subdomain remember to ‘Manange Redirection’ in order for your subdomain to redirect to the correct page.
An addon domain is an additional (secondary) domain of your main site. Use addon domains to host additional domains on your account. For more information, read the documentation.