When you've created a mail address through your control panel we send you a mail containing the login details of your address.
You can use these to log in to our web mail environment. For this you can visit our webmail at https://transip.email. Next, fill in your mail address as username and the password which we've sent you. You can then use the webmail environment to send and read e-mails.
For the usage of the webmail you can consult our manual here.