Event on dynamodb create or update

I want to trigger a function when my serverless table have an update or a creation I saw this part in the doc

      - stream:
      type: dynamodb
        Fn::GetAtt: [MyDynamoDbTable, StreamArn]

But I do not really understand the part Fn::GetAtt: [MyDynamoDbTable, StreamArn] what is GetAtt and StreamArn

I also saw some code using existing events but I can not use it as I am having dev and production environment

Fn::GetAtt is an AWS CloudFormation intrinsic function used to get an attribute of a Resource. See AWS Documentation

In this case, It’s retrieving the StreamArn property of the MyDynamoDbTable resource.

StreamArn is the Arn(Amazon Resource Name) of a DynamoDB Stream. A Stream is the method a DynamoDB Table uses to emit events in response to Create/Modify/Delete actions similar to SQL triggers for onInsert/onUpdate/onDelete.

Hope it helps.