We do the trade via wifi by exchanging friend codes so I need your friend code and you need to add mine. You can find yours and add mine in this section of your 3ds.
My friend code is 2638-3343-9173 and my trainer name in Pokemon is Chaos
After we exchange friend codes, you need to go online in the PSS section of the game, you can do that by clicking the internet button in this section
You know that you are online if you see random passerby online around the world.
Then just wait for a trade request from Chaos then we trade the Pokemon
Take note that you need random Pokemon that you won't need for the trade. For example if you purchase 6 Pokemon, you must have 6 random Pokemon that you won't need to complete the trade.