Any ideas, images, or words you do not create yourself must be given proper credit if you use them in your paper, BECAUSE you are using someone else's intellectual property. It shows you have academic integrity and honesty, and helps your readers find your information sources. It shows where your information came from, and adds credibility to your paper.
Online documents make it very easy to copy and paste information without thinking and without giving proper credit. Make sure you understand how to cite your sources.
When it is time to gather all of your notes and start writing the paper, avoid the most common mistake - plagiarism. Plagiarism is not only taking large parts of someone else's work and not attributing credit to that author; paraphrasing sections of a work, even using synonyms and citing the work, is also plagiarism.
Even if the ideas are rewritten, the source of the idea must be cited and the author given credit.