In the United States, intellectual property can be owned. Once you write down your idea, record it, draw it, perform it, or put it in some tangible form, it belongs to you; it is copyrighted. As the owner of the copyrighted material, you have the right to decide you can:
Fair Use allows the use of portions of copyrighted creative work in educational settings without first obtaining permission for the purpose of criticism, comment, news reporting, teaching, scholarship, and research.
When you use the ideas of someone else, you must give credit (called citing) the authors of those ideas.
If you do not properly cite the sources you use, you may be guilty of plagiarism.