Final answer:
Clicking the Close button in the upper-right corner of an application window signals the application to close. The application will typically prompt you to save unsaved work before shutting down, although specific behavior can vary.
Step-by-step explanation:
When you click the Close button in the upper-right corner of an application window (often represented by a red X), the application will typically begin the process of closing. This action sends a signal to the application that the user wants to terminate or exit the program. Most applications will respond to this action by attempting to close any open files, asking the user to save any unsaved work, and then shutting down.
However, the specific behavior might vary depending on the application itself. Some applications may minimize to the system tray rather than completely closing or might prompt the user with additional options. It is also worth noting that if the application is not responding, clicking the Close button might not immediately close the application and you may have to use the Task Manager or Force Quit (on Mac) to end the process.