After logging into your Joomla dashboard you will see its home page with all your free Joomla sites listed.
To access your website click on its name in the Dashboard:
To access the admin panel of your Joomla! website just click on the Access Admin button on the Joomla.com dashboard:
You can also use the standard admin login page of Joomla, located at name.joomla.com/administrator/ (where name should be replaced with your own website subdomain) to login. Learn more in the Joomla admin username and password tutorial.