There are many ways in which you might meet Pokémon during your adventure, such as meeting Pokémon traveling with other Trainers or coming across Pokémon in the field. If you use the DexNav, those everyday Pokémon encounters can also be used to register Pokémon in your Pokédex.
You’ll be able to check where the Pokémon you see reside in the wilds using the distribution tab in your Pokédex. If you see a Pokémon you like, try to go out and catch one! The feeling of realism in your adventure is getting a great boost!