Different values assigned to the Pokémon you capture will quickly tell you how the Pokémon will perform in battle, and these stats are a bit different than the ones you're likely used to in traditional Pokémon games. For example, what does CP mean? Let's break it down.
What does CP stand for?
In Pokémon GO, CP stands for "Combat Power" and is entirely separate from the Pokémon's Hit Points (HP). While the two usually correlate (meaning a higher CP will yield a higher HP), the CP is important if you want to use the Pokémon in battle.
A Pokémon with a higher CP will perform better than one with a lower CP. While you can use type advantages in a lot of instances to help you take down a Pokémon with a higher CP, if there's too big a difference it won't do you any good.
As your personal level gets higher, you'll be able to find more powerful Pokémon in the wild — which, in turn, will make your team more powerful and allow you to take on more challenging battles and raids.
Your Pokémon's CP will never be lowered, though its HP will be during a battle.
There are ways to increase your Pokémon's CP, similar to how leveling up a Pokémon works in the traditional games.
How to increase your Pokémon's CP.
To increase a Pokémon's CP, tap the Pokémon you want to power up and click the "Power Up" button below its stats. So long as you have enough Stardust and candies for that specific Pokémon, you should be able to power it up with no issue.
If you don't have enough Stardust, we have a guide on how to get more. There are also plenty of ways to get more candies, like making the Pokémon your buddy and walking with it or catching more of the same Pokémon. Transferring a Pokémon to the professor will also give you more candies, though you should be careful not to transfer the Pokémon you plan to power up, as you will not be able to get it back once you do.
Evolving a Pokémon will provide the biggest jump in a Pokémon's CP, so if you can find a lower-evolution Pokémon with a high CP, you'll spend less Stardust and candies making it a powerful player on your team. Even if you already have an evolution of a certain Pokémon, if you have the lower-evolution Pokémon with a higher CP, it may be worth it to spend the candies to evolve it.