The best analogy for me would be to use something the person you’re explaining to already uses. For example, if they’re a reddit user, I just say imagine everyone has the capability to create their own reddit website, and everyone’s reddit sites can be interconnected and you can choose to join whichever site you want and see content from the other sites. If they’re coming from twitter, just change the it from reddit to twitter. It’s much easier than using the email analogy.
It’s mainly on facebook messenger for me. You’re right that it’s really hard to keep tabs on family/friends with a feed that’s full of stuff you’re not even following or subscribed to. So by “keeping tabs”, it’s actually just being able to keep in touch via messenger. Other than that, I use marketplace to sell stuff, but that’s it.