Shutter speed is a measure of how long the shutter of camera remains open when taking photo. It is measured as a fraction of second. For example - 1/15 is slower shutter speed While 1/60 is the faster speed. Slow shutter speed (More light falls on sensor) is used when you want blur in your photos (e.g. Smooth Waterfall) Fast shutter speed (Less light falls on sensor) is used when you want sharp photos (e.g. sharp image of any moving object) So if you want brighter photos, keep shutter speed slower. Also when shutter speed is slow, you need to use tripod otherwise photos will come out blurry.