On Route 30 you will battle Pokémon, here is a list of them.
Caterpie
Pidgey
Metapod
On your way to Mr.Pokémon's house you should stop by a man's house with a tree outside. You can get 2 berries, one from the tree outside the house and one from the man, who will share one with you.
If you want to get to Mr.Pokémon's house you have to keep to the right side route. When you get there you will see a tree with a PSNCUREBERRY on it.

Go in to Mr.Pokémon's house and Pro.Oak will give you a PokéDex and Mr.Pokémon will give you a mystery egg and restore your Pokémon's HP.

After getting the PokéDex and going outside Pro.Elm will ring you and tell you that someone has stole a Pokémon from the Lab and tells you to go back to the lab.(this is where that person at the window comes in)
On your way back to the lab you should heal at the Pokémon Centre before you go back through route 29. Then as soon as you try to go to route 29 a person wants to battle(Rival).

He was the one who stole the Pokémon from the Lab, so this is what he has.
Your Pokémon/ Rival's Pokémon
Cyndaquil Totodile
Totodile Chikorita
Chikorita Cyndaquil

After the battle heal and head to New Bark Town.