You don't need to have _original_ ideas. You can summarise the ideas from some other source (or, ideally, sources). In summarising, you make some choices as to

You don't need to have _original_ ideas. You can summarise the ideas from some other source (or, ideally, sources). In summarising, you make some choices as to what you think is important, and what you think is immaterial. You explain the core concepts in your own words, maybe differently from the source material. And, if you're quoting from a specific source verbatim, you acknowledge it. Plagiarism is not about the copying in and of itself. It's about appropriating somebody else's work and pretending it's yours.