After your first pokémon battle at Lake Verity, you and your friend go to return the pokémon to Professor Rowan.
Meet Professor Rowan
As you enter Sandgem Town, Dawn or Lucas will meet you. During the cutscene, Professor Rowan allows you to keep the pokémon that you chose. You have the option to give your pokémon a nickname.
Next, say Yes and the professor will give you the Pokédex, which will automatically record data about the pokémon that you encounter and catch.
Go With Dawn or Lucas
Go outside and Dawn or Lucas will show you the Pokémon Center, which has a red roof. You can go there to heal up your pokémon.
Next, they show you the Pokémart, which has a blue roof. You can buy items there that will help you in battle and in the field, and you can also sell items to get more Pokédollars.
Optional: Buy Poké Balls
You will get some free Poké Balls soon, but if you want to, you can buy Poké Balls now in the Poké Mart (the blue-roofed building), which will allow you to catch pokémon in tall grass. If you buy 10 Poké Balls at a time (or a multiple of 10) you will get one free Premier Ball per 10 Poké Balls. The Premier Ball works the same way as a regular Poké Ball, but just looks different.
Visit the Pokémon Center
Go into the Pokémon Center (red-roofed building) and talk to the person behind the counter to heal up your pokémon.
You can use the blue computer to the right of the counter and choose "Someone's PC" to access the Pokémon Boxes. This is where you can store pokémon if you don't have enough room in your party.
Go can go upstairs to visit the Local Club. The person on the left can change how you appear to others when you are in the Union Room. You can talk to the person in the middle to enter the Union Room, where you can connect with nearby players. The person on the right says that the Colosseum is not ready yet.
Feel free to go into houses and talk to people in Sandgem Town before you continue.
If you go south from Sandgem Town, you enter Route 219, where you will find an Antidote in the southwest.
Go Back Home
Go outside and go west to Route 201. If you want to catch some pokémon, you can go into the tall grass (see below for tips for catching pokémon). You can catch Bidoof and Starly here. If you would rather avoid the tall grass for now, then go south from the 201 sign to jump down the one-way ledge. Go west from there, then take the north path, and when you have gone past the tall grass, jump down the ledge. Then you can go south to return to Twinleaf Town.
Go into your house and talk to your Mom. During a cutscene, she gives you the Guidebook. You can check it anytime in the Key Items section of your Bag. It contains useful information about how to do things in the game.
Then your friend's Mom gives you a Parcel to give to your friend.
Go outside and your Mom will remind you to wear your hat. You will also get a Trainer Card that you can see from the X menu.
If you wish, you can go to the Key Items pocket of your Bag and select the Guidebook, then Register it. This will allow you to access it by pressing + or -.
To Jubilife City
To get to Jubilife City, you will have to go back through Sandgem Town, so go north from Twinleaf Town, then go east until you can't go farther east, then go north through the tall grass, then go east to reach Sandgem Town.
Tips for Catching Pokémon
To catch a pokémon, you can throw a Poké Ball at it by pressing X, but there is a chance that it will break out of the Poké Ball. You can improve your chance of capturing the pokémon by reducing its HP until its HP bar turns yellow or red. Also, eventually your pokémon will be able to cause status effects. Status effects like Sleep and Freeze improve your chance of catching the pokémon. Other status effects (Poison, Burn, and Paralysis) improve your catch probability, but not as much as Sleep and Freeze.
Rest your pokémon in the Pokémon Center, then you can optionally check the map on the wall of the Pokémon Center to see that Jubilife City is to the north. When you are ready to go there, go north from Sandgem Town to reach Route 202.