They don't really need to understand the federation to use it in practice, same as here on lemmy, and same as email. Most people don't actually understand how email works or that it's federated, they just know to put the right @domain.com at the end and it works for them. If you attempted to explain how email works to someone, it'd sound really complicated and off-putting to non-techies too, but if they know just enough to make it work, it seems simple.

I'd only explain it to people who are curious enough to ask about it. Otherwise, all anyone would need to do is just direct new users toward the Movim site, create an account (no email required, just a username and password), and bam, they're up and running right in their browser and can start connecting to friends. All they need to know is a username or the name of a group, which is in the exact same format as email so it'll already feel familiar (Person@domain[.]net, or InterestingHobby@domain[.]com).

Since it doesn't need an email and works right in the browser, it's really quick to try. Why not give it a shot with a friend for a bit to see if it could work for you?