The White Forest is in pokemon white and Black City is in pokemon black. They are the same thing but the only difference is you can't catch pokemon in the Black City but you can muy lots of cool stuff. In a nutshell they are the same thing but just a little different bacause of the different games.
U can talk to people in white using enter link and then a city gets build and u can battle
You trade 50 peolple and talk to a spy in Pokemon center castelia city
You have to interact with a friend's copy of Black or White via Entralink. Then you have to go to their Black City or White Forest and talk to the trainers in their City/Forest.
Talk to a guy in black city.
You have to interact with a friends game through Entralink and talk with the trainers in their Black City/White Forest.
In Nimbasa City to the top left of the Pokemon Center there is a house with a blue haired kid in it. Talk to him for Strength.
Go into Shady Alley in Castelia City. Talk to the man behind the dumpster and he gives it to you.
Search around in Nimbassa City and go into all the houses and talk to people. It is found in Nimbassa city
You get strength in Nimbasa City in a building there. I am not positive on where it is exactly, so talk to everyone in the buildings there and you will find it.
Find someone who owns Pokemon Black and use the Entralink to enter their Black City. Talk to people in there as they may want to move to your forest (which in turn makes grass and trees appear in the forest)
You must know someone with Pokemon Black and travel through entralink and talk to her shes near the entrance against the east wall in Black city and sometimes she will come its all luck of the draw
You have to get the event Celebi on Pokemon Diamond, Pearl, Platinum, HeartGold, or SoulSilver, then use the Pokemon transfer in Pokemon BW to get in in BW. then you have to talk to somebody in Castelia City.