Recently alot ask me what is ISO how to use ,i think it's best to have a lesson here as well,i wont goin to write everything again as there are alot link outside the internet that offer good information on the 3 golden key. Here a good link to expose and learn about Shutter speed,ISO and aperture. Basically ,you need to find the right exposure but using the three factor and it can be dynamic variant on either factor to form the right exposure. This mean if ISO low you can compesate it with a slower aperture and speed to get the correct exposure.If Aperture is high you can compesate it with slower speed and higher ISO. Image it 's like a Triangle shape which each changes on the value affect each other.
basic concept in learning photography
do practise in the simulator.
Any enquiries just ask here i'll try reply.