“ELI5: What’s the difference between proprietary and open source”
Here’s the way to think about it.
Think of proprietary as a completely written book. You can’t change any part of the story in the book without permish and also can’t “steal it”, with writing the story and contents on a Google Doc, you’ll still have to buy the book for 10-20$
Think of open source as an empty book. The kernel made by Torvalds is just the pages the cover, etc. You can get a certain kind of customizable story(distro) with unique font style(desktop), while some distros are REALLY empty(look at Gentoo and Arch), and others are REALLY full(look at Ubuntu and Mint). Even with a full story(e.g. Ubuntu), you can still edit the story, the fonting, etc.