Here’s an online web-based camera simulator…
Most critical – the relationship between aperture and shutter — here.
Camera shake simulator
Film speed sim (for Digital, there’s an equivalent setting)

In a nutshell; to get a perfect (or good anyways) exposure, you need three critical ingredients, aperture, shutter and ISO/ASA (or film speed). For film users, ISO (or ASA) is set by the film you buy. In digital, that can be changed so you have three settings to play with. Remember that if you reduce aperture, you will need to increase something else to compensate. Think of it as a balance scale. For a set ISO, shutter speed and aperture value, you have a nice exposure. Reduce shutter speed and you might need to increase aperture to get the same exposure. Exposure = amount of light needed.

ISO/ASA (or film speed) tells you how much light you need. Shutter and aperture controls the amount of light you get. Like a faucet, larger aperture (smaller value!) means you turn on the tap larger, shutter speed tells you how long you keep the tap open. Longer means more water (or in this case, more light).

Relationships:
Shutter speed: numeric in fractions of a second or seconds, higher = longer. i.e.:
1/500s or 1/125s or 1/30s to 1.0s or 5.0 seconds.
Aperture: numbers called f-stops, lower number = bigger aperture. i.e.:
f/2.8 = large aperture, f/4 = smaller aperture, f/8 = small aperture
ISO/ASA : film speed or digital sensor sensitivity. Larger number = more sensitve, less light needed. i.e.:
ISO 100, ISO 400, ISO 800..