Here's the breakdown:
* Friendship: Pichu's friendship level needs to be high enough for it to evolve. You can increase friendship by battling with it, feeding it berries, and petting it.
* Leveling Up: Once Pichu has high enough friendship, it needs to level up to evolve. You can level Pichu up by battling wild Pokemon or training with it in the gym.
It's important to note that Pichu cannot evolve into Pikachu by just leveling up alone. The high friendship level is crucial.