The calves are made up of two main muscles, one that is emphasized when the knee is straight and one that is emphasized when the knee is bent. So, an exercise like standing calf raises or donkey calf raises works one and seated calf raises works the other. There is also a muscle on the front of the shin that pulls the toes up that has a small effect on the overall visual look of the lower leg.
That said, calves exercises seem to be the ones most often performed with atrocious form. Full range of motion and complete dead stop at both extremes is essential to shock these muscles to grow. During normal daily activities, such as walking or running, the calves perform a lot of repetitions but seldom are used in the extremes of their range of motion. Go all the way to a full stretch at the bottom end of the motion, come to a complete stop, pause using the muscles on the front of the shin to force an even fuller stretch, and then accelerate to full extension at the top of the range of motion and again come to a complete stop and flex the muscle with a pause. A couple of properly performed sets of 12-15 reps is all that is needed to stimulate maximum growth. I like to alternate seated and donkey calf raises on subsequent sessions to keep it short and interesting.
