I still think the fediverse is using language that most people don't understand. My cousins, let alone my parents, won't understand half of what's written there. Federation? ActivityPub? Instance?
The best comparison I've heard that everyone I've explained it to seems to comprehend is that the fediverse is basically email 2.0. You can send emails with only pictures, text, video, or all the aforementioned together. In order to do so, you need to pick a server, just like you do with email, but in the fediverse they aren't "google", "aol", "yahoomail", but "lemmy.ml", "feddit.it", "mastodon.social", "chaos.social", "kbin.social", "kbin.pub", and others.
You will notice that "lemmy.ml" and "feddit.it" look very similar, but have different names - that's because they run the same software called lemmy. "mastodon.social" and "lemmy.ml" look very different and have different features, and that's because (you guessed it!) they run different software (mastodon vs lemmy). It's just like GoogleMail runs different software than YahooMail, has very different features, but can communicate with each other.
The fediverse is the same, just with 2 major differences: it uses email 2.0 (aka activitypub) and the software is opensource. That means developers (or anybody who wants to for that matter) can see the source code of the software. This is unlike Google, Yahoo, Yandex, AOL, who keep their source closed.
In the fediverse, the different software focuses on different things. Lemmy presents the fediverse to you like reddit, mastodon like twitter, peertube like youtube, diaspora like facebook, and so on and so forth. The great thing is, they can all talk to each other using email 2.0 (aka activitypub)! Therefore somebody on a server using mastodon can view post made on a server running lemmy with a video hosted on a server running peertube and comment on that video, right from their server that runs mastodon!
So please, pick a server with the software and conditions you like and have fun on the fediverse!