The Beginning

Phoebe found the Book of Shadows in the Attic, and Prue and Piper didn't believe her when she said they were witches and they had magical powers. Then Piper discoved her freezing power Prue and her Telekinisis and Phoebe's first Preminition. They are the Charmed ones and nobody can change that.

Others

Prue died! The Power of three was now the power of two. Then Paige Mathews walked into the picture. Patty Halliwell their mother had another girl with her whitelighter and now Paige lives with Piper and Phoebe and learns her power orbing. They are now the power of three once again. The Charmed Ones.

Oh yeah I almost forgot Piper got married to her whitelighter Leo and now they have a son Wyatt.