Select the 'Configure Screensaver' option from the tray icon to open the screensaver settings. The Choose Screensaver menu is quite nice, it takes you to Windows' select screensaver screen. This does not put the computer into sleep mode though as it turns off the monitor only. On the other hand, if you want to save power, the 'Turn off monitor' will likely be your favorite option. The first option lets you Start the screensaver instantly this also works when you double-click on the icon. Right-click on its icon and you will see a pop-out menu. The program's name should give you a hint, as it runs from the system tray. And it has a couple of extra features that you may find useful.
If you want to start the screensaver immediately, TrayBlank is a nice tool.
