You can login to the WordPress management by area adding /wp-admin/ at the end of your domain name, on your browser. On the example below simply change the value "www.yourdomain.com" for your registered domain name:
The WordPress login form will appear, insert your username and password. If you don't want to enter your login details on each visit, you can check the Remember Me option. Now click on “Log In” and you will enter to the WordPress management area.
Keep in mind that the WordPress username and password are those you have configured during the installation process. It is not the same data for login to MrDomain.
Note: some plugins can modify the URL for the WordPress management area, if you use one of them you have to use the personalized URL.