On your exposure mode dial there is an aperture priority mode and a shutter priority mode.
In aperture priority mode, you pick the aperture (f-stop) and your camera picks the shutter speed.
In shutter priority mode, you pick the shutter speed and your camera picks the aperture.
The problem with these modes is that, in terms of exposure, you wind up with the same brightness of a standard exposure.
If you’ve ever had the experience of perceiving your picture of being too dark or too bright it’s because a “standard” exposure is not what you need to get the “correct exposure” for your picture.
You’d get the exposure you needed if you picked you exposure setting in manual exposure mode and intentionally brightened or darkened your picture using aperture, shutter speed or even ISO.
Learn more about exposure.