I love these learning modules from the Microsoft. As I understand you are using the next learning Module: https://learn.microsoft.com/en-us/learn/modules/connect-an-app-to-azure-storage/ Correct?
First, you need to activate the sandbox.
After you activated it, some parameters will be auto-populated in your script in the txt on the left side. You only need to copy the script, add your unique storage account name and paste to the Azure Cloud Shell on the right side. After that just run the code (click enter).
A Storage account name. The name will be used to generate the public URL used to access the data in the account. It must be unique across all existing storage account names in Azure. It must be 3 to 24 characters long and can contain only lowercase letters and numbers.
Please let me know if this is the exactly place where you stuck while going through the module.