what a crappy analogy, but oh well...

well.... i know you're hungry at the moment... so let's start cooking!!!

How about having some Maggi Mee?

Let's say cooking a packet of Instant noodles at full flame is going to cost you 3 minutes of your time. But oh no... wait a minute! you need 5 minutes to enjoy puffing a cigarette before your meal. Now your noodles gonna get soggy because its going to get overcooked by the time you finish your cigarette, so you adjust the flame to half-flame (for example).

Now, in photography terms, how long you leave the noodles on the stove is the Shutter speed. Too short then it's terrible to eat, too long then it's over cooked. The right amount of time is the right exposure. But wait, that's not all, how your noodles turn out also depends on how intense you set the flames to. So it's how long you set your pot on the stove & how intense the flames are. So while the duration of how long you set to cook is the Shutter Speed, then the flames must the Aperture. Now do you understand the correlation between these two?

ISO? That's the third factor to determine how your noodles get cooked. Umm... let's just assume ISO is the thickness of your pot. With everything else the same, the thicker your pot is, the longer your noodles get cooked... But if your pot is thinner, it's going to be more sensitive (higher ISO means higher sensitivity), so you need less time.

Anyway cooking your noodles for 5 minutes with half-flame and cooking your noodles at 3 minutes with full-flame will get your noodles cooked, but to some people, it doesn't taste the same, so in photography terms,- go figure!!!

HAHAHA....

As to directly answer your question where Exposure = Shuter Speed??

You probably adjusted a parameter called Exposure Compensation. As your camera sensor on Automatic mode tries to determine the proper combination of ISO, aperture, and shutter speed to get what it feels the "correctly" exposed picture, you as a photographer might evaluate the scene differently from what the camera suggests. So now, Exposure Compensation comes into the picture. Let's say you want your noodles soggier than what normally people like... so you either turn up the heat more, or leave it to cook longer... similarly, your camera does the same. It automatically adjusts the "levers" to get what you want.

optimumly, regardless how fast the shutter speed is, the brightness of the image should stay the same because your camera will automatically tune the other "levers" (Aperture & ISO) to ensure your picture is exposed properly. Only exception is on Manual mode where changing Shutter speed does not affect the other "levers" and the end result is a darker picture.

So if you select a faster shutter, the camera compensates by increasing ISO, or opening up the Aperture wider (Back to Maggi Mee example, shorter cooking time cooked compensated by having a bigger flame and ummmm... thinner pot). Only when the max ISO or widest aperture is reached, and you still aren't allowing enough light to enter, then only the image becomes "darker" or underexposed. (Yes, there's a max to how big you can get the fire to be, isn't there?)