Yep, all you have to do is turn off your monitor. I told you it was easy.
You can conserve energy with the push of a button. Most people leave their monitors on when they leave the desk, relying on the screensaver without realizing that the screensaver uses just as much energy as the monitor in normal mode. Using a screen saver also actually causes the computer to use more energy. Flying through that crazy maze and making those flowers do the Cha-Cha forces the computer to access its memory, costing it power.
Some people use their hibernate function. Your monitor isn't actually turned off in hibernate mode. The computer is partially powered down, but often, the monitor is still active. It can't tell the difference between projecting tons of colors or projecting tons of blank.