The relationship between copyright and plagiarism can seem complicated.
Plagiarism is about using creative work without attribution ("giving credit"): Plagiarism is using someone else's words (or other creative output) and claiming them as your own or otherwise not giving them credit. It is to avoid plagiarism that we cite sources (among other reasons) and provide attribution for quotations and paraphrasing in our work.
Copyright infringement is about using creative work without permission. Copyright infringement happens whenever we use someone else's creative work without their permission. Does that mean that every time we quote someone in our papers we need to ask for their permission? No! This is because the copyright law has a concept called "fair use" built into it. You can read all about fair use elsewhere in this guide but the kind of quoting that you would do in a paper would nearly always be a fair use.
So, it is possible to plagiarize without infringing copyright. It is also possible to infringe copyright without plagiarizing.
Nearly any use images, video, or audio are allowed in class presentations are made in face-to-face classes in a classroom setting is permitted. This broad exception does not apply to copying and distributing text so doing something like photocopying an article might not be allowed.
We are often asked by students or student clubs if it is okay to show a movie. There are, basically, two contexts in which you could show a movie without public performance rights (the license that allows you to show a movie legally in public when you are not the copyright owner): in your private home (as long as you're not opening it to the general public or charging admission) or in a classroom as part of a class. For virtually all other showings you will need have public performance rights in order to show a movie.