To create an email account, first login to your myCP. Depending on your account type, you will need to do one of two things:
On the Email Admin page, you will find a listing of email accounts by domain that are attached to the particular account you are working with (depending on the account type you have and its configuration). You may either click the "Users" link to the right of the domain you wish to add a user to, or you can also click on the domain name itself, which will present you with a page with more relevant information about the mail configuration of that domain, along with links to manage it, including the same "Users" link as above.
On the following Users page, you will find a list (if any) of the users currently set up for the domain you have selected, and at the bottom of that box, you will find a link for "Add New User". Click that link, fill in the relevant information, and your account is now set up and ready to send and receive mail.