Academics are all about you growing as a person, learning to think like a scholar and learning how to integrate the two. When you are learning to be a scholar, the first thing you do is find out what has been done before. You hear lectures, read books and articles, etc. Most new information is then integrated somewhat into what you think about topics.
When you formally talk about topics as an academic (even as a student), writing papers or essays for a test, you need to discuss where your new ideas came from and how they were developed. That is the purpose of citations.
It is not wrong to talk about ideas that came from other people, this demonstrates that you have read what has been done in the past and helps to give credibility to your thoughts. Scholar X had a theory about ….. and I think it can also be applied in this situation to solve this problem, or to explain a phenomenon.
Always use a citation to indicate any ideas that are not your own. Citations include both an in-text citation such as a parenthetic reference, a footnote or end note (or a caption if in a presentation) as well as a listing in the Bibliography or Reference List. Don't forget that anything copied directly needs to be in quotation marks and have a citation. Citations are not just for written papers, you should cite your sources when creating a PowerPoint presentation, or other multimedia presentation.
If you didn't do the work, don't claim the work. This is applicable to papers, presentations, and using your own answers on tests and quizzes. It also applies to purchasing or "borrowing" another person's assignment. It applies to images and software code as well; cite it or do your own work. Cheating applies to the sharer as well as the borrower. Don't share work with someone (either a test or an assignment) that you know they are planning to pass off as their own.
Group work can be confusing: Whose ideas are whose; and What can everyone use in their individual reports; vs. What should I write on my own? If you work on a project together and don’t have individual responsibilities to report on, you should write up the group’s conclusions in your own words based on your ideas about what you found. You might also be asked to give your opinion in support, or not of the group discussion. Check with your instructor for more guidance on how to delineate your efforts.