James Corbet just posted another very good and instructional video addressing those of us who are new to figuring out how the world really works as opposed to how many of us think it works.
A portion of the video is dedicated to how James feels about the permanency of the internet or, more accurately, the information stored on the world wide web. He thinks much of it, meaning the content pumped out by us "conspiracy theorists", will be obliterated by the-powers-that-be-in order to control the narrative. Personally i'm not so sure about that, but i will concede that this is a possibility. In that light i would recommend, as James does, that we all store the important data which we discover on-line.
What James doesn't tell us, other than to do a search, is exactly HOW to grab the data we want to store and so i shall provide some brief suggestions in that regard, limited to my personal experience.
When you come across content you want to save, the most obvious solution is to press Ctrl+S and your browser will guide you through the process. You can save textual and imagery content this way, but not video. If you want to streamline the process, you can install a browser extension. For instance, the Firefox add-on repository (AMO) has several add-ons you can use to save content, one of them being SingleFile by gildas.
Saving video is another matter and while there a plethora of browser extensions that can accomplish the task, i would highly suggest avoiding all of them and using youtube-dl instead. youtube-dl can be installed on multiple platforms including Linux and Windows and it can save videos from many more video sharing websites than just YouTube. If you can find the link to the actual video however, such as a URL ending with .mp4, .avi, .mov, etc., then you don't need any extension because you can just press Ctrl+S or right-click the link to save it. For many video sharing websites such as YouTube, Vimeo, etc., it either isn't easy or is simply impossible to find a single source for a video and so youtube-dl is a wonderful tool in these cases because it goes way beyond what Ctrl+S can do.
I would also highly recommend archiving any content you want to save on an archive website. The best archive service i can recommend for textual and image content is archive.today. They don't obey robots.txt files (or at least not completely) and so once you archive something with them, it *should* be permanent. The next best service, and one that works for virtually all content including videos, PDFs, etc., is archive.org. While the WayBack Machine, as it's called, will not archive videos embedded in a page, one can use it to archive videos separately. If you create an account you can have your own archive library if you wish. Here's mine.