WIndow management in Filemaker is different depending on whether you are on Windows or Mac computers
Adjust WIndow [Maximize]
will pop all windows open for the current file out to their maximum sizes.
In some cases (at least on windows systems), this is not desirable as you may have small dialog type windows that you don't want resized this way. Then you may need to use the Move/Resize Window script step with Get functions that will return the current screen width and height to specify the window dimensions. On windows systems, that maxes out the specified window to fit just inside the Filemaker application window.