After you get back to Pallet Town, head into the lab again. Talk to Professor Oak. You deliver the Parcel, which Oak identifies as a custom Poké Ball, and your rival bursts in. Oak explains that it was his life's dream to collect data on every Pokémon in the world, but that he has grown too old to accomplish it. So, he asks you and Blue to do it for him. He gives you each a Pokédex, which contains images of Pokémon you've seen, what they sound like and where to find them in the region, if possible. If you've owned the Pokémon for any length of time, the Pokémon's height and weight, as well as a short description are added. He wants you to do this for all 151 Pokémon. Blue boasts that he can accomplish the feat without your help, and that he will borrow a map from his sister to do so. You may now exit the lab once more. You may, if you choose, visit Blue's house (the house to the east) and talk to his sister to obtain a Town Map from her. However, this is NOT recommended, because you can only hold seventy different types of items between your bag and the PC, and they do fill up quickly. Furthermore, if you catch a Flying-type Pokémon, it will eventually learn a move that can be used outside of battle as a map and more. You will have room in your inventory to collect redundant items like this at the end of the game. Feel free to stop by your own house. If you talk to your mom from this point forward, she will heal your Pokémon. Finish up in Pallet Town and go back to Viridian City. If you want to fight for some extra goodies including some Pokémon for your new Pokédex, head west onto Route 22. Otherwise, head north onto Route 2.
The first thing to do upon entering any town is to head to the Pokémon Center, where the nurse will heal your Pokémon for free. This restores their HP, PP and status. In the northeast corner of the Center is a PC. Not only can this one store items, but it can store Pokémon as well, up to 240 of them. If you have access to another Game Boy with Red or Blue Version and a link cable, you can battle or trade with them by talking to the attendant on the right. After finishing up at the Center. Head northeast to the Pokémon Mart. Upon entering, the clerk will identify you as being from Pallet Town, and give you Oak's Parcel, which you need to deliver to him. You can't buy anything until you do, so exit. One more thing you can do here is walk clockwise around the clump of trees in the northwest part of town. Examining the cuttable tree with A will yield a hidden Potion. Next, head back to Pallet Town.