Shooting handheld photography has many benefits. You can get more angles quickly; it's lighter and more compact, and you can experiment more with various creative angles. The downside is that you can't shoot HDR, long exposures, or night photography. 

Back in the old days, with film cameras, the shutter was a mechanical device in front of the film that would open and close for a set time, exposing the film. Even in motion pictures, you can notice the effect the shutter has on the picture. Typically, a film is shot at 24 frames a second with a 1/48-second shutter. But if you remember the fight sequences in Gladiator or even storming the beaches in Saving Private Ryan, they shot with a fast shutter to stop the motion, so everything looked crisp and real versus having that soft motion blur you get with a 1/48 shutter.

In Digital Photography, the ISO is the setting that adjusts how sensitive your camera's sensor is to light. It usually ranges from 100-64,000+ on most cameras. The higher the number, the less sensitive it is to light. This means that if your ISO was set to 64,000, you could expose a candle-lit dinner accurately. However, if you were outside on a sunny day, your ISO must only be set to about 100. So, the ISO is what the camera uses to measure how much light hits the sensor.