When it comes to apertures, what you should know about them is that they control two things in your images. The first is how much of your image is in focus or not. They work very much like your eye’s iris. In low light, your iris widens and in bright light, your iris closes up to adapt to all the light coming in. And with that said, your aperture also controls how much light comes in–and is therefore an exposure parameter when shooting.
Reddit user VeeDees recently made a gif illustrating the effects of depth of field on your images. As you can see, the image starts all the way at f1.8 and goes down to f22. By F22, you can see much more of the scene being in focus and not blurred out by bokeh.
Because of the way apertures work, there also can be diffraction that happens–and that all depends on the size of your sensor. With full frame 35mm cameras, diffraction starts to happen at f8-11. But with Micro Four Thirds cameras with a 2x crop factor, it begins to happen at around f4 and f5.6.
The gif showing how aperture affects Depth of Field is after the jump.