They are so happy and excited to have been able to grant your request, that the email says “Your Your Developer Edition domain eltoroit-samples-dev-ed.my.salesforce.com is ready for testing.” I guess they meant to say: “Your! Yes your! Developer Edition domain is ready”. So let’s finish up the process…
Login back to the ORG, and take a look at the current URL. In my case it says https://na30.salesforce.com/home/home.jsp take a close look at it and get ready to say bye-bye na30, hello MyDomain.
Go back to the My Domain page (Setup | Domain Management | My Domain), and get ready to click on the [Click Here To Login] button, notice the URL where it now reads: “https://eltoroit-samples-dev-ed.my.salesforce.com/domainname/DomainName.apexp” aren’t you excited? Isn’t this the greatest thing? Let’s share it with everybody in your organization… so click on the [Deploy to Users] button.
A messagebox is displayed alerting you that “once you deploy your new domain name, you can't reverse it. After deployment, all users will be redirected to your new domain”. But after you have chosen a great name which was available and you have tested it… Why would you want to reverse it?
You could now configure the My Domain Settings, so click on the [Edit] Button for the [My Domain Settings] and set the Login and Redirect policies as needed. The section [Authentication Configuration] allows you to change the login page to add your own logo, the contents for the frame on the right picture. In my case, this is what my login page will look like: