In daylight, the cones do all the work. In darkness, it's the rods that come into use. They let you see the outlines or silhouettes of objects, but they can't pick up much detail. Many nocturnal animals, such as owls, have rods but no cones. Other animals, such as some rodents, have cones but no rods and are virtually blind at night.
Humans have both rods and cones.