Aperture / Shutter Speed
You know: it’s (almost) all about Aperture and Shutter Speed! If graphs help you visualize the relationship between the two, have a look at these.
Just keep in mind: photography is not about the numbers. It’s the numbers that are about photography. Work towards associating numbers with the creative effect they will have on your images: shutter speeds give you motion blur (blur in time), aperture means depth-of-field (blur in space).