The interesting thing about these two scales is that they do the same thing mathematically but have completely different effects pictorially. The trick is to decide which combination will produce the picture you want. Basically, these settings work against each other. So, with a certain amount of light, you give up depth of field in order to stop action, or you sacrifice action for depth of field. Typically, unless you're using special film, you can't have a maximum of both.
Film comes in different sensitivities, which are referred to as film speeds.
Ah, I've never understood that. You'll notice that the speeds of various films have numbers that look nearly the same as the shutter speed scale. This works out nicely when measuring the light and deciding the film, f-stop, and shutter speed combination you require. Of course you also need some way of gauging how much light there is. Most cameras have built-in light meters, but there's actually an inverse square rule in effect for a direct light source.