The f-stop, or aperture, is one of the key camera settings every photographer must master because it controls two critical things: the amount of light going through the lens and how deep the field of focus (depth of field) goes in your image.
The larger the opening of the lens, the more light hits the sensor, but the shallower the depth of field. The smaller the opening of the lens, the less light hitting the sensor but the deeper the depth of field. It’s a pretty simple concept, but there are numbers involved, which leads to math, which make it seem more complicated than it really is.
Along with your shutter speed and ISO setting, your aperture is part of the “exposure triangle.” Adjusting each of these settings can give you a variety of different effects.