Firstly you need 2 Nintendo DS Consoles
They can be a 3ds/XL ,2ds, Ds Lite, DS, DSi or DSi XL
You load Pokemon Soulsilver onto DS no.1.
Then you load either Pokemon BW or BW2 onto DS no.2
In-Game Requirements
You need to have beat the game on Pokemon BW/2 to get to the Poke-Transfer Lab on Route 15
It is a one way trade so its bye-bye to your Pokemon on Soulsilver
Poke-Transfer
You go onto the Poke-Transfer on Pokemon BW/2.
Open DS download Play on DS no.1 where you have Soulsilver.
It should come up with a Poke-Transfer Data Tool
Now after you have downloaded it onto DS no.1 a mini game will launch on the Soulsilver.
It's like Angry Birds but Pokeball version. You just catapult Pokeballs onto the Pokemon that peek out the bushes. You have a time limit
(I find this game incredibly annoying though)
After you catch/grab all the Pokemon
You can send 6 Pokemon over at a time. If you don't catch 'em all they get sent back to SS . So no pressure :)
There will be a message popping out about how its a one-way transfer. Say Yes/Ok/Confirm
(Can't remember exactly what it does)
After your SS Pokemon should go to BW/2
This Video will help
But its not finished !
You have to go through Process of Bank.
Now assuming your BW/2 cartridge is not a digital version you'll have to download your Pokemon onto Pokemon Bank via Poke-Transporter. It is included in your annual fee for Pokemon Bank.
Its quite simple you just download the Pokemon from BW/2 onto Pokemon Bank.
Another Video
The Final Point to ORAS
This video will show you how
