I don't know how to give the link reference of the site .

You can do it by copy the link of the image where you take it such as google, blogs or else and then paste in under the photos. And it's better if you know name of the photographer (they usually add watermark, but it's okay if they don't). Have you done the achievement task for newcomer? You'll find the way from the guideline's post on Achievement 3 and 4.