The long shutter is used for long exposure shots.  This is mostly used for dimly lit environments, such as night photography, or shoot pics that depict motion.  For example, you can capture light trails from a car driving my the camera the shutter is open.  My recommendation is to use a tripod or set the camera on something stationary.  With every jitter or shake of your hands, the picture will be blurry.

So here’s how you get to the long shutter setting.

1.  Start getting to the Program Mode.  If you’re in Auto(A), use the scroll wheel to get to Program(P) mode.

2.  Press the Func/Set button.

3.  Press the DISP button.

You should now have the option to set the exposure duration.  It ranges from 1 – 15 seconds.

Here’s a sample of capturing light trails.