How do you mygrate the Pokemon from another game?

How do you mygrate the Pokemon from another game?
Trade through game link cables =O

Unless you're referring to the transfer of LG/FR (I think R/S, too) Pokemon to Diamond/Pearl and Platinum.
Then you would have to fill out your pokedex to unlock the Pal Park in D/Pzperiodz
Then when you go to the pal park you can choose up to 6 Pokemon to transfer a day into your D/P game.
Well actually, you choose at the game's title screen menu thing.
You can select "Migrate from (gba game title here)" ... THEN you go to the pal park and catch them.
You don't really have to do anything fancy...just throw the balls at them and they'll come back without a fight.
And it's not hard to fill out your dex (you don't have to fill out the national dex).
Every Pokemon you need to fill out the dex can be seen in that game.
Just make sure you battle everyone.
Including the Elite four plus 1.
You probably have to defeat the Elite four, as well, to unlock the pal park...I can't remember...but it would help if you defeated them, anyway lol
It makes things easier.