http://en.mimi.hu/photography/iso.html

Basically the higher the ISO you set the grainier the picture. You'll probably have to put your camera into Manual mode for it to be able to change. Everyday pictures are shot at usually 50 ISO where night shots are usually done at 400+ ISO depending on camera.


1/3 rule
http://www.shutterfreaks.com/Tips/RuleOfThirds.html