ISO

ISO is one of the photography basics which refers to the light sensitivity of the image sensor of your DSLR. ISO stands for International Standards Organization, a name which carried on from the days when film was used.

The lower the ISO, the lower the light sensitivity, therefore, the darker the image. So in outdoor sunny shots, ISO60 or 80 is recommended. On the other hand, the darker indoor shots would need higher ISO. You can use lower ISO's in darker settings provided you use some form of flash or external lighting.

Here's the catch; the higher ISO you go, the higher the noise volume would be. That would mean a grainier image. So it is recommended to keep your ISO as low as possible and adjust only as needed.

(The image on the left uses ISO100 while the image on the right uses ISO400. You can notice the increase in noise in the close up as the ISO increases. Good thing about Automatic Modes is that shutter speed and exposure settings adjust as you change the ISO when using ISO priorities)