>>3150405> I'm not 100% sure what an f/2.2 is, but just setting my camera to the lowest it goes, which is 4.5, my pictures come out dark. From what I understand, a lower f/number means a bigger lens, and that lets in more light.What you need to know about the f/number is that it's (as you say) related to the size of the lens opening (not exactly "a bigger lens"). A smaller f/number means a wider aperture, which lets in more light, and gives you more background blur (i.e., less is in focus).
The technical details behind it is that it's the ratio of the focal length (that's the "f/" part) to the size of that lens opening. So if you had a 50mm lens with a 50mm diameter lens opening, that would be f/1.0 (50/1.0 = 50). If you had a 50mm lens with a 25mm diameter, that would be f/2.0 (50/2.0 = 25).
Long ago, people discovered that this ratio, of the focal length to the diameter of the lens opening, was what determined how much light got in, and it was the same across all lenses in terms of exposure. So f/2.8 on one lens lets in the same amount of light as f/2.8 on another lens, even if one lens is a 35mm and the other is a 400mm.
It is difficult to make lenses with wider apertures. Both physically (more glass, higher quality glass, tighter tolerances) and in terms of design (the wider the aperture, the harder it is to design a lens that focuses all of the light exactly right across all wavelengths, so they need a lot more corrective lens elements), so lenses with wider apertures tend to be a lot more expensive (although the aperture vs. cost equation is complicated and multi-dimensional and is affected by things like whether or not the lens is a zoom, whether or not the company making it is willing to put out a shit lens, what format the lens is for, etc).
So yeah, your lens is probably the cheap kit lens that came with your camera, and it only gets to f/4.5 max at the focal length you're using.
