Evolotion

Evolotion
Evolotion makes pokemon stronger.

Levels
Leveling up is one way. This is the most common way.

Stones
When you use a stone like Leaf stone a pokemon may evolve, then they can't learn Moves by themself.(With some exeptions)

Link Trade
Pokemon may evolve when you trade with a real person.

Friendship
Making pokemon like you can make them evolve when you level them up.

Other
There are other ways too.