Go down stairs in any pokemon center and the lady behind the counter should introduce you to the Wifi environment and give your your pal pad and friend code.
If you have already done this and dont remember your friend code then go in your key items pocket of the bag and find your pal pad, your FC should be listed there.
Last but not least its not an obligation to have a friend code in your trainer card, you can have one without, it will just list zeros.