接続できない
You're trying to log in to the wrong type of Salesforce org. You can only complete hands-on challenges with a Developer Edition org.
Try again with a Developer Edition org, like a Trailhead Playground. Make sure you’re not using a production or sandbox org, or an org with a namespace assigned to it.
I followed what was shared in the article but it did not work as well. However, it started working today when I tried it again. Perhaps the answer to this issue was to wait
DE環境にはSandboxはない
I don't think you can create sandboxes in Developer org.
If you are a partner of Salesforce and develop Apps for the App exchange - then you can sign up for a Partner Org which will have Sandbox Instances.
See the below links for more info,
http://wiki.developerforce.com/page/Partner_Development_%26_Test_Environments
http://www.salesforce.com/partners/overview/
https://developer.salesforce.com/forums/?id=906F00000008sZ0IAI
組織にPlaygroundスターターアプリがありません
DE環境にインストールしたけど使えないです。
注意: このツールは Trailhead Playground 専用です。 本番組織では利用できません。