Ok heres what you have to do to catch pokemon kinda easy.

1. get a pokemon with an attack that paralyzes pokemon.
2.get ultra balls
3.battle the pokemon that you encountered
4.use the paralyze attack you have
5. weaken it with weak attacks(if stronger that you use strong ones not too strong)
6.when the bar turns red catch it.

sometime all you have to do it just paralyze it.