In basic terms ISO is the level of sensitivity of your camera available to light. The lower your ISO, the less sensitive your camera is to light and vice versa. The benefit of a high ISO number such as 3200 is that in low light environments your sensor can capture images without using flash. However this can lead to images looking grainy or having more ‘sound’ to them. If you use a high ISO number in a environment that has good lighting it will cause the image to appear ‘blown out’ which is basically when way too much light is exposed to the sensor and causes a white effect.
Here is an example of this that I took:
The image at the top uses a ISO of 100 which is a pretty standard ISO to use. But as you can see the image at the bottom which uses an ISO number of around 1600 has the blown out white effect.