Aperture is space through which light passes in an optical or photographic instrument, especially the variable opening by which light enters a camera. It can determine the F stop for a photo. A small F stop such as 3 would be a shallow depth of field whereas a f stop such as 23 would be a deep depth of field.
It affects depth of field directly. Using a low F stop means that more light is entering the lens and therefore it doesn't need to stay open for as long. Using a high f stop means that less light is entering the lens and therefore the shutter speed will need to stay open a little longer which mean a slower shutter speed.