When you are creating teaching materials using other people’s work, you must consider the copyright of that work.
If you create lecture slides that contain images, figures or text that you didn’t create personally, then you are copying these works, and your use will involve copyright.
If you upload copies of articles, book chapters or reports to your course site for your students to read, then you are communicating these works, which involves copyright.
This doesn’t mean that you can’t use other people’s work. But you will have to check to make sure that your use is permitted.