What is evolition?

it's where a Pokemon has to have a certain item needs a certain move,needs traded, or has to get to certain lv.(level) to change into a similar form.Some Pokemon can evolve more than once(example: turtwig evolves into grotle and grotle evolves into torrterra)but some Pokemon can't evolve(example:groudon,dialga,and ditto)you can stop an evolution by pressing B while they evolve.Hope I helped:):):):):):)