First, you need to take the screenshots and/or save QR codes of your patterns. If you need help with that, let me know. After you've done that, you go to the browser, which is located on the 3DS main menu. You can leave New Leaf running in the background if you want, it makes no difference. Then, once in the browser, you can use the image hosting site of your choice to upload your images. Let me know if you have any questions.