To get into this sex position, a couple need only get comfortably into Missionary and then, when it feels good to do so, the partner on the bottom can bend their legs around their partner.
More About Toad Position
The Toad sex position wins points for being simple and effective.
This position can be difficult if one or both partners carries extra weight on the front of their bodies. The size and weight of the partner on top is also a significant factor.