You can exit SparkTrust PC Cleaner Plus by clicking the X in the upper-right corner. By default you are given an option to fully exit the program by clicking the Exit​ button, or to minimize the program by clicking the Minimize button.

If you have set the program to minimize you can fully exit it by right clicking the icon in the system tray, and selecting Exit. The system tray is the area on your start bar where icons are displayed, next to the clock.