In several windows of MoStacks you do not only handle a single object as the single stack in the Edit Stack window, but a whole set of objects, e.g. the set of all backgrounds in the Edit Backgrounds window. All these windows use the same system to handle the objects based on modes:
There is a list on the left that shows all objects of the given type that exist right now in the current stack, e.g. a list of all backgrounds. Selecting an entry of this list displays the information about the object and switches the window into the View/Modify mode.
There is an output field that shows the currently active mode, in the top/middle area of the window.
Now you can modify the object by changing values of fields and controls in the window. Each mode-based window has a Modify button to save the changes and make them permanent. Or, the other way round, nothing is changed until you click this button, and you can close the window or select another object without problems. If you forget to click the Modify button, changes are lost.
In the View/Modify mode the Delete button is enabled, and you can use it do delete the currently selected object.
To create a new object, you have to switch to Create mode first. You do that by clicking the New button. After you specified all necessary information about the new object, click on the Create button to create the object.
Nothing really happens until you click the Create button; if you forget to click and close the window or select another object first, you won't get any new object, and the information you entered will be lost.