Twinleaf Town is the players home town in Pokémon Diamond and Pearl and Pokémon Platinum. This is the first time that there is not a Pokémon Lab in a starting town. It has four houses, the house in the bottom right hand corner is the player's house. The house in the upper left hand corner is the rival's house. Twinleaf Town also has a small lake at the very bottom. (Later when you get the HM move "Surf" you will be able to get a Odd Keystone at the small lake if you surf until you get to the mid part of where the trees are, press A and you will get a Odd Keystone.)
You have just watch the episode of the Red Gyarados. Then head downstairs and your Mom will tell you that your rival is looking for you. She also warns you not to go into the tall grass. Then head outside and go to your rival's house at north-west.
Blocked Route 201
You cannot access to Route 201 unless you have spoken to your rival.
Meet Your Buddy
Head to your friend house located at northwest of Twinleaf Town. When you reach the entrance, your friend will knocked into you. Then he went off and went back again to take the things he forgotten. You enter the house and go upstairs, you will see him packing his things. He will then run downstairs again. Meet him at Route 201.
After the Pokémon battle and meeting Professor Rowan and his grandkid, you will return home. Your mother tell you to meet Professor Rowan at Sandgem Town and gives you a Running Shoes. Now head to Route 201 and began your journey to Sandgem Town!
After Visiting Sandgem Town
Head home to tell your Mom about the big quest you are going to do. Your Mom will then gives you a Journal. Then your friend's Mom will enter. She will gives you a Parcel that your friend forgotten to take. Head to Jubilife City to pass him the Parcel.