Type Effectiveness

 Every Pokémon has an assigned type, and sometimes they have two. The type assigned to the Pokémon will allow you to figure out what it is strong against and what it is weak against. Knowing about type effectiveness is very important when participating in battles against other trainers, completing raids, or taking over gyms. 

A Pokémon with a single type will be most effective when using a move that is the same type because it will gain extra attack power. This is called STAB (Same Type Attack Bonus). For example, a Water-type Pokémon using a Water attack will have increased damage by 1.5 times. When using this attack against a Pokémon that is weak to water, a Fire-type, for example, it will increase the damage by another 2 times. Below is a chart that fully shows type effectiveness among the 18 types available.

                            (Chart is from Pokémon Database (pokemondb.net))

On the lefthand column, you will see that it represents the attacking Pokémon. Going right from one of the types, like Fire to Grass, for example, you will see that Fire is super effective. If you reverse this and go from Grass on the left to Fire, you will see that Grass is not very effective against Fire, but not completely useless like Electric would be to Ground. 

As mentioned before, choosing a party of Pokémon to battle with depends heavily on type effectiveness. But, it is also different depending on what you plan to do. If you want to do regular battles against other Trainers or Team Rocket, you will want to diversify which Pokémon you bring with you. For example, you don’t want to just bring 3 Fire-type Pokémon, as a single Water-type Pokémon could potentially wipe out your team. When looking at the defensive side of the chart, you will see that Steel is extremely well at defending against most types, so having a Steel-type is a good way to help protect your team (minus Fire, Ice, and Ground attacks). But, if you plan on taking up a raid where the selected Pokémon is Dratini, for example, you should only bring Pokémon that you know will be effective against Dragon-types (Ice, Dragon, Fairy).