Hey there, Pradip Jaliya
The Azure Sandbox is built into the modules. So, depending on the module you are doing, you will see an option to create a sandbox environment for you to use.
So, on Unit 3 (https://learn.microsoft.com/en-us/training/modules/create-windows-virtual-machine-in-azure/3-exercise-create-a-vm) of the training module you have linked, there is a puzzle for you to complete that will create your virtual machine for you after it checks your eligibility
After it has created the sandbox for you, you can proceed to follow the instructions. It may be that you must navigate to https://portal.azure.com and sign into your account. Once you have signed into your account, please click onto your name on the top-right corner.
Then click onto Switch directory
After this, you will see your directories that the account is connected to. You should see the Microsoft learn sandbox listed as a directory. You will need to click onto switch directory. Then, follow the instructions in unit 3.
Hope this helps,
Nathan