To unlock the ability to evolve your Starter Pokemon and other team members, you will need to first beat the main story. While we won’t go into spoilers, make sure that you have beaten the story and then you will get the ability to unlock Pokemon evolution.
If you need help with this, be sure to check out our walkthrough.
How to Evolve Pokemon
Once you have beaten the main story of the game, head to Whiscash Pond north of the Pokemon Square. To evolve a specific Pokemon, make them the party leader and have them enter the Luminous Cave alone.
Pokemon that evolve simply from leveling up will be able to evolve there so long as they have already reached the required level. Other Pokemon that usually evolve through different methods like a stone or other item only need Evolution Crystals to evolve.
You can find these in tough dungeons in the post-game or by buying them from shops in dungeons. It typically takes either two or four of these to evolve specific Pokemon.
How to Mega Evolve Pokemon
Mega Evolution requires a Pokemon that can Mega Evolve like Charizard or Groudon. You need to use an Empowerment Seed to accomplish this, which can be bought or found in dungeons.
The Mega Evolution will last for the duration of the dungeon, so be sure to save it for when you really need it like tough boss fights or dungeons.