Hi John,
If you want to perform the steps of the simulation in real life using your own subscription, you need to first create the resource group. In the simulation, you can see the resource group already exists when they first open cloud shell.
To your specific question, please see excerpt from New-AzResourceGroupDeployment documentation:
The New-AzResourceGroupDeployment cmdlet adds a deployment to an existing resource group.
Please click Accept Answer and upvote if the above was helpful.
Thanks.
-TP