Okay, well wifi trading isn't much different. You have a Pal Pad, which is in your Key Items. From that you get your Friend Code, and that's what other people register in their Pal Pads, so they can trade with you. When you and the other person are ready to trade, go to the Pokemon Center and up to the second floor. There, head to the middle receptionist and enter through there. When the other person arrives, you'll see them in the bottom part of your screen with the name you gave them.
To invite someone to a trade, head up to the screen and click "A" and choose from the menu. To exit the invite, click "B". Most people prefer you keep the chatting function off, so be sure to click "X" when you enter.
To accept someone else's invite, just click on their sprite if they're hopping. That means they're inviting you.