Avoiding plagiarism in articles?

[Den]

Ok, so I wrote an article for a magazine, and they rejected it saying that it was copied from the internet. However, I never copied anything from internet, but I did some research from the internet. It was necessary to do some before writing something. I think I never cited sources that's why they rejected it. How can I cite sources in my articles? One more thing, I found two or more articles in their magazine which were directly copied from the internet. Those two articles were written by two different authors, but in that magazine they were shown as written by one author!! It is interesting that they accused me of plagiarism, when in fact they are the ones who are plagiarizing. I feel like I have been scammed, and my article is gone in some nasty hands!!