In Pokemon Go, you can level up your Pokemon, no matter if it is a starter or one you can find in the first few areas you play in. Sadly, your starter is much harder to level up in comparison with Pokemon you can find nearby, so you might be willing to focus on them rather than on Charmender, Squirtle and Bulbasaur.
CANDY AND STARDUST
You have two different items to level up your Pokemon, Stardust and Candy.
Stardust is an item you can you use to both power up and evolve your Pokemon, and it is very valuable. Talking about Candy, it is an item every Pokemon has in its unique type. Charmender has Charmender Candy, Bulbasaur has Bulbasaur Candy, and so on. You can handle the power up and evolve process from your Pokedex.
Candies are a bit rare, so you can farm the type of Pokemon you want to level up most and this process will grant you many of them. You can transfer the Pokemon you don’t need anymore using the “Transfer” option, but beware: you will lose the Pokemon forever. Nevermind, anyway this will allow you to get those precious candies you wanted desperately.