• Professor Elm's Lab
After the character creation process, you will find yourself in your room in New Bark Town. Walk downstairs and you'll be stopped by your mom, who will give you all the menu items to use. You may want to play with the options at this point, but nothing is really necessary.
Leave your house and your neighbor and friend, either Lyra or Ethan, will briefly introduce themselves. Head next door into Prof. Elm's lab. He requests that you take a Pokémon with you and walk with it for his research. Shortly after, he receives an E-mail from an acquaintance of his about a discovery. Naturally, he's too busy and requests that you go see what it's about.
All the starters are roughly equal, but the game will be harder should you choose one over the other. Cyndaquil makes the game much easier, given the enemies you'll encounter, while Chikorita will make it much harder. Totodile is a good average choice.
Before leaving, Prof. Elm's assistant will give you five potions to assist you on your journey. Exit the lab and your friend will recommend you show your new Pokémon to your mom. She wishes you good luck on your journey and gives you your Pokégear, which you can use to make calls on. Now, feel free to leave New Bark Town. Prof. Elm will stop you before you get too far, and give you his Phone Number. Calling him normally isn't all that helpful, but he'll call you every now and then.