As you can see in the illustration presented below the two types of receptors in the human eye are quite different in their structure and functions.
Rods (grey) are more sensitive to light and there is a convergence of the output of their signal. Because they possess only one type of pigment they can only distinguish between black or white ( light or no light) and form less precise images.
On the other hand, cones (red) are less sensitive to light, but they possess three types of pigment which enables them to distinguish many different colors and form sharp images.
