Did you ever wonder why your fire type Pokemon faints when facing a Rock type Pokemon? Each Pokemon has its own type. Sometimes a Pokemon has two types. An example of this would be that Bulbasaur has grass and poison. A Pokemon will have a type advantage if the opponent has a type that is weak against the Pokemon its facing. A Squirtle's Water Gun attack can take down a Charmander easier then the Charmander using Ember to take down the Squirtle. This is because Water has an advantage over Fire. With double types, such as a Charizard which has both fire and flying, it could cancel out a weakness or make it a normal attack against them. A Charizard is weak to electric attacks because it is part flying.
A Pokemon can also have a double weakness. A great example is Mantine. Mantine is a both a water and a flying type Pokemon. This means an electric attack, like a thunderbolt from a Raichu will most likely take down the Mantine because electric type attacks have an advantage over both flying and water Pokemon. Some types of Pokemon do not have much for weaknesses or advantages. So a Meowth, a normal type Pokemon has no advantages but is weak against only fighting.
Type weaknesses could be used to your advantage, if you know you will be facing a Pokemon trainer with electric type Pokemon, then you should bring a Dugtrio to battle the trainer. Dugtrio is a ground Pokemon and has an advantage over an electric types. Try to make your team of Pokemon vary in types so you will be ready for any Pokemon battle thrown at you! This is the best strategy you can use while choosing Pokemon you wish to train and battle with. A well balanced team will make every battle an interesting match. You should highly consider in using Pokemon types to you advantage if you want to become a Pokemon Master!