Try to visualise what's happening in your mind mechanically rather than getting confused with numbers.
In simple terms..
Aperture:
Think of the lens and the aparture, the larger the aparture number the smaller the hole in the lens (the iris), this means less light can get in. So, to compensate for that, you would either decrease shutter speed (allowing light in for longer) or increase ISO (sensor/film sensitivity).
ISO:
How sensitive the film (or sensor is). The higher the number the more sensitive. So, if you have ISO 100 and it's a little dark outside, you can either increase the ISO (so the sensor is more sensitive but will make the image more grainy the higher it gets) or decrease the shutter speed. Or, open up the lenses eye (aperture) to let more light in there. A combination of the three is what you need.
Shutter Speed
Shutter speed is how quick the shutter opens and closes. In the camera, the light is let in for the amount of time you want. So, if you are in low light again, you can either decrease the shutter speed which will make moving things blurry because the light is streaming in until the shutter close, or increase the Aperture or increase the ISO allowing for a faster shutter speed to freeze frame the action better.
The way to juggle these is to know what you're shooting. If you're shooting a static scenic view then you can get away with a long exposure (keeping the shutter open for longer). That way you can have a lower ISO (which is better quality, less grainy) or open up the lens (opening the aperture, lenses iris). The problem with opening up the lens's iris is that some lenses don't produce as good quality shots when they are fully open. So, you close the iris a little (say F8) and then leave the ISO at 100 (not very sensitive but good quality pics) and just leave the shutter open for a long time (30+ seconds). This means enough light will get to the sensor so it can properly expose the picture.
If you were to use the set up above in a club, the pic would be a blurry mess because people are jumping around and the lights are changing. So, for that scene you would want to open the lens right up (quality may take a hit as iris is really open but in those low light situations it's usually necessary). Then increase the ISO to 1600 (or more but it gets really grainy) which will allow you to use the shutter fairly fast meaning it will blink in a fraction of a second and capture that freeze frame of action. The open iris (say F2.8 aperture letting in a lot of light) and the high ISO (sensor really sensitive, records light very quickly) means that a faster shutter speed can be used.
In nice normal light, like walking around a local park on a summers day - if you were shooting ducks on the pond. I'd say you should use ISO 100 (the day is bright so a lot of light will be getting in meaning you can use a lower ISO) then stop down the lens (meaning to start closing the iris) to F8-F11 which will be a comfortable range for the lens giving good quality. Then your shutter speed should still be nice and fast as it's a summers day. This should allow you to freeze frame the ducks in the shot.
After you can visualise what's going on in the camera, it's pretty easy to figure out what does what. When you're comfortable with that, you should go on to learn about exposure and metering modes.
Others may have better examples though, hope this helps and doesn't confuse you more!
