I try to teach my mother how GUIs work and it's really hard. It's hard enough to teach her that pressing "X" closes the window, but then she opens something like a web browser and it has "X" on every tab, which gets her confused. And worst of all, she can have email client on top of the web browser, which adds additional "X" to think about.

Perhaps keep them clear of the idea. And stick to Windows. Assuming they can do Window management...

I've an 84 year old family member, who still doesn't get tabs. Heck they don't really get the Web. And are kind of stuck in their Web Email client. I got an alarming call one day saying they'd hosed all their emails. But it turned out they'd failed to log into their email account, ended up creating a new one, and then wondered why their inbox was empty.

Perhaps relate it to tabbed folders in a file cabinet?

...or good old-fashioned recipe cards. Most card files were arranged with tabs, but a box of recipe cards would be more than familiar to anyone my age or older. (You'd pretty much have to have lived out of cans and/or on restaurant meals to have avoided them.)

Or a rolodex or a card catalog in the library... these are where the idea came from.