The Game Sync is a feature located in the C-Gear of Pokemon Black/White (C-gear is the thing-a-ma-bob on your touch screen). Simply tap "Wi-Fi" after you've met Fennel and completed the side task that comes with meeting her (Saving a Muna in the forest next to Stratation). You'll see "Game Sync" come up on your touch screen. Tap it. You will connect to Wi-Fi and be given a code. With this code, you can connect to the Pokemon Global Link website, and put your Pokemon online in the "Dream World" (Basically an in-browser game where you can play with the Pokemon you uploaded and transfer/grow berries to your game). But first you need to make an account at the Pokemon Global Link website, so do that first to save time.
And that's about all there is to it. Click here and you will be transfered to the Pokemon Global Link website.
And please, forgive me if I mis-spelled something about the cities or Pokemon names. I'm still learning the new city names and Pokemon names.