There is nothing better than the great natural light of early morning or evening, but we don't always have that light or the sun doesn't cooperate and is in the wrong place. That is where having a reflector comes into play.
A great shot with excellent back lighting and key lighting.
Reflectors come in all sorts of shapes, colors and sizes, but the principals are the same. Reflectors are meant to redirect and/or adjust the properties of light for an intended subject. This allows you to achieve the desired shot out of the camera and reduces the amount of post processing needed.
A typical multi-reflector set with (left to right) black, gold, white and silver reflectors