You've already heard the warnings about plagiarism. Obviously it's against the rules to buy essays or copy chunks from your friend's homework, and it's also plagiarism to borrow passages from books or articles or Web sites without identifying them. You know that the purpose of any paper is to show your own thinking, not create a patchwork of borrowed ideas. But you may still be wondering how you're supposed to give proper references to all the reading you've done and all the ideas you've encountered.
The point of documenting sources in academic papers is not just to avoid unpleasant visits to the Dean's office, but to demonstrate that you know what is going on in your field of study. It's also a courtesy to your readers because it helps them consult the material you've found. That's especially important for Internet sources. So mentioning what others have said doesn't lessen the credit you get for your own thinking—in fact, it adds to your credibility.