Older fixed focal-length lenses (and some current ones) have an aperture scale engraved on them next to the focus-distance scale. Some zoom lenses even have curved lines along their barrel that form an aperture scale for their focal length range.
Shutter speeds are arranged in a similar scale, so that one step in the shutter speed scale corresponds to one stop in the aperture scale.
As you move up the aperture scale settings (1,1.4,2,2.8 etc..), the less light that is let in. Bigger the number, the smaller the amount of light that gets in.
EV1 requires half the amount of exposure, EV2 a quarter and EV3 an eighth and so on. Each full stop on the aperture scale (1.4 - 2 - 2.8 - 4 etc) represents a doubling or halving the exposure, ...
 See also: Aperture, Scale, Photograph, Lens, Film
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