Echo was a woodland nymph that agreed to help Zeus. Zeus wanted to spend the day with other nymphs but he suspected Hera was watching. Echo was known for talking a lot so she agreed to help Zeus by distracting Hera while Zeus did his thing. Hera figuring out that Echo was stalling her and cursed her by making her only be able to repeat the last word or phrase she heard. She could only repeat.
Meanwhile, Narcissus was on a hunt with his hunting pals. Narcissus' prophecy was that he would live a long life as long as he did not come to know himself. On his hunting expedition, he passed a pond and stopped to drink out of it. When he goes to take a sip out of it, he catches a glimpse of himself in the reflection of the water.
After Narcissus saw himself in the pond, he wouldn't stop staring. No one could take his eyes away from the reflection. He rejected anyone that tried to talk to him and was extremely rude to them all.
One person who tried to get Narcissus' attention was Echo. But the problem was Echo could only repeat what she heard. Echo was extremely lonely and had no friends, so she was hopeful Narcissus could be her friend. Unfortunately, Narcissus was too busy staring at himself to consider using manners when he spoke to people, so he made Echo sad and hibernate in a cave.
Shortly after this Narcissus' body rotted away and he left behind daffodils where he died. Also, Echo's depression caused her to stay in the cave until she too dies. In her place was ashes and stalagmites. The myth of Echo and Narcissus explains the natural phenomenon of stalagmites, daffodils, and echoes.