Copying phrases without citing.
Copying sentences without citing.
Paraphrasing without citing. (Putting an idea into your own words.)
Summarizing without citing. (Giving an overview of another person's ideas.)
Copying charts, graphs or videos to use in your presentation without citing.
Reusing an assignment you created for a previous class in your current class without permission from both instructors (Self-plagiarism).
Copying an entire paper.
Purchasing an entire paper from a web site.
Sometimes asking a friend/relative/classmate for help on your paper can also result in plagiarism, depending on how much and what kind of help that person gives you.
Bottom line: If you use someone else's words, ideas, or creative work without citing it, you have plagiarized.