To handle user input in a GUI application:

1. Event-driven programming: Use an event-driven approach, where the application responds to user interactions like button clicks, key presses, or mouse movements.

2. Widgets and controls: Utilize GUI widgets and controls like text fields, buttons, and checkboxes to receive user input.

3. Event listeners: Attach event listeners to widgets, which trigger specific actions when an event occurs.

4. Input validation: Validate user input to ensure it meets requirements, such as checking for valid email addresses or numeric values.

5. Error handling: Display error messages or feedback for invalid input, guiding the user to correct their input.

6. State management: Update the application's state accordingly based on user input, such as changing a label's text or enabling/disabling buttons.

7. Callbacks: Use callbacks to perform specific actions after user input, like executing a query or sending data to a server.

By following these steps, you can effectively handle user input in a GUI application, creating a responsive and interactive experience.