This is yet another explanation of the exposure triangle. What caught my attention in this post by Andrew Childress on PhotoTuts+ is the bucket analogy.
Here it is is:
One way to understand this is to imagine filling up a bucket. The size of the bucket is the ISO. 100 ISO is a big bucket needing a lot of water to fill up. How far you turn the faucet handle is the aperture, and how long you leave the water on is the shutter speed. F/2 for example is a wider aperture, a gushing faucet. F/16 is a narrow aperture, a dripping faucet.
In order to fill the buck with F/16, you’ll have to leave the faucet on for a long time. That is, unless you have a very shallow bucket, like ISO 3200.
This analogy is very helpful for some people, for others it’s just confusing. If you’re confused, that’s alright, just keep moving on.