DialogManager is a manager that mainly focuses on controlling the whole life cycle of each dialog. It will load panel, initialize panel, use pre-defined transition to show panel when DialogManager.open() is called. While for DialogManager.close(), it will find out which panel is going to be closed, validate the result of onSubmit() or onCancel(), and use pre-defined transition to hide panel.
Basically, this DialogManager will be only used accompanied with DialogService. If you want to know more details about how they are communicated with each other, you can go check settings/js/modules/dialog_service.js for more details.