The sandbox is available in every module that contains a hands-on Azure exercise. Each unit includes a prompt at the top of the page to indicate the sandbox status. It initially looks like this:
Selecting the Activate Sandbox button starts the activation process. If this is the first time you've activated a sandbox in Microsoft Learn, a second prompt asks you to accept the license terms. To accept the terms, you need to sign in with your Microsoft account, such as an Office 365 or Outlook.com account. If you don't have one, you can create one for free. The system then creates a new sandbox for you. It takes no more than 5 minutes.
After the sandbox is activated, you'll see a prompt that says you have access to a sandbox.
Your browser will show you when you are in a sandbox. See the image below: