This select dropdown allows you to either connect to an existing stage that exists within this environment, or to create a New Stage. If this is a new deployment, then the only option will be to create a New Stage, and so this should be selected for new deployments. It is common, however, that you may wish to "reconnect" to an existing environment, where you would then just select that stage in the dropdown. After you have done this, your stage will now be "connected" to the backend server and all changes made to forms and resources within that stage will affect that remote project.