how to trade pokemon from other regions in black?

Answer 1

There is a transfer station that you can access once you beat the Elite Four. From their, you can receive Pokemon from Heartgold/Soulsilver Versions, and also Pearl/Diamond/Platinum. To get Pokemon from Ruby or Sapphire, just transfer them into one of the older games.

When you find the building in one of the routes, you have to have two ds's, and you play a target shooting game where you need to stun you Pokemon and then capture them.