Most, but not all pokemon have evolutions and to evolve they need to level up by battling. Winning a pokemon battle whether that be in the wild or against another trainer earns xp points that are needed to reach the next level. Let's take a look at the evolution below of charmander that we saw in the main page.
It's clear to see that charizard on the far left seems a lot stronger than charmander on the right and evolving does in fact increase a pokemons stats which is helpful for winning battles. For most pokemon that can evolve twice like charmander here, the first evolution takes place at some level between 15-17 and the second at some level between 32-36. What's especially cool about evolving is the fact that pokemon can learn new powerful moves.
I personally think that the process of evolving a pokemon is fun because it shows you what kind of pokemon it can beat and which it can't. I'd give pokemon games a 10/10. I'm also writing this last paragraph to make sure I have three paragraph chunks. Thanks for reading.
Here are some important things to consider when trying to win a battle.