How is the return object in a Python-AWS lambda used?

In lambda function templates appear the return object

def lambda_handler(event, context):
   
    return {
        "statusCode": 200,
        "body": json.dumps({
            "message": "hello world 2",
        }),
    }

I couldn’t find any documentation about how this object is used.

• How must be configured?
• What fields are mandatory?
• When and how is it used? Can be consumed by other services?