In the battle of Crecy, about 8,000 - 10,000 English archers shot about 500,000 arrows to kill 15,000 - 20,000 Frenchmen. These numbers are very speculative, but the proportions are probably correct.
The objective was for as large a group of archers as possible to shoot arrows into the sky, from where they would come down on the enemy. Any hit was a good hit if it took an enemy soldier out of the battle, whether the arrow hit the enemy soldier's foot or the flank of his horse.
Archery practice meant learning the proper angle to shoot the arrow into the air so it would land a certain distance away, and of course learning to pull the heavy, 100 lb or so warbows. If there were enough arrows in the air landing more or less 200 yards away, some of them would hit the enemy soldiers who were advancing at that distance.
At one time, it was required of all able-bodied Englishmen to practice archery, but forbidden to practice at distances of less than 100 yards. No point in training people to get too skillful in taking the king's deer!
The thing that puzzles me is that from about the time of King Henry VIII to well into the 1700's, the longbow was actually more effective than the musket: it could get off more shots per minute, had a longer range, and you could fire it in the rain. And yet the musket quickly replaced the longbow on the battlefield almost from the time it was invented. I don't know why that happened, other than the musket made a lot more noise and was a lot easier to train people on than the longbow.