Once you gain access to Route 15, you can go to the Poketransfer Laboratory. Once there, you'll hear how it works and the restrictions. Here's what you need to know about the Poketransfer process.
Restrictions
1) No HM moves allowed. Pokemon that have HM moves are unable to transfer
2) No items. You'll be prompted to put items in your bag (on your other game) before proceeding.
3) Spiky Eared Pichu is untransfereable.
Notices
1) Pokemon transferred are unable to be traded back to previous gen games. THIS PROCESS IS A ONE WAY TRANSFER.
2) Pokemon not caught in the minigame will not be added to your Pokemon Black/White.
3) You can redo the process as many times as you want.
4) Transferring your Gamestop Celebi or WIN2011 Shiny Entei, Raikou, or Suicune will allow you to participate in the Zorua and Zoroark events, respectively.
Minigame
How to play: You'll be armed with a pokeball-firing bow. The Pokemon sprites will jump from bush to bush, and you have to catch them as they jump. If they poke their heads out of a bush, fire a Pokeball at the bush to make them jump. After catching all six within the designated time alloted, they'll be added to your PC. IF you miss any, they'll be returned to the PC on their respective game.
Conditions that can occur: Confusion, Sleep
Confusion: If two Pokemon jump into one another, they'll be momentarily stunned. Use this opportunity to catch them while stunned.
Sleep: Hitting the pink fluff that will drift across the screen will put any Pokemon outside of a bush asleep. You can catch any sleeping Pokemon. The pink fluff will only come once, so time your shot wisely.
This will help anyone who is unfamiliar with the Poketransfer process or minigame.