You will be sent a welcome mail with login instructions upon account activation. In case the mail is no longer with you, it is possible to resend from your Client Center.
Below is how you can login your account:
To access your cPanel, you can go to yourdomain.com/cpanel
To access your Webmail, you can go to yourdomain.com/webmail
To access the Client Center, you can go to this page.
Don't forget to replace yourdomain.com with your own website domain name.