Step 1: (Optional) Add Metadata Components to an Org Using the UI

If you’re starting with a new practice org that doesn’t have customizations, you only have standard metadata that can’t be retrieved. To use the Metadata API retrieve call, add a component on the Salesforce UI to your practice org. If you’re working on an existing project, you already have components to retrieve and can skip this step.

From the Object Manager tab in Setup, click Create | Custom Object.
Enter an arbitrary name for Label and Plural Label.
Save the component.