Instructions
Travel to Kotobuki Town.
Enter the building to the left of the Pokemon Center. The Pokemon Center is easily located because it is the only building with a red roof and a giant Pokeball on it.
Talk to the woman behind the counter.
Choose the first option to gain access to the GTS room. The game will automatically save.
Use the computer in the room. From this computer, you can place Pokemon on the GTS or browse through the Pokemon others have put up to trade.