If you install the Element app, its first-launch is quite simple and newbie-friendly. There are a couple more "options" than e.g. WhatsApp, but they're presented very clearly: "Join millions free on the largest public server" or "Premium hosting for organizations" or "Custom & advanced settings" -> tap the first + free one -> Sign up / Sign in with a totally-normal experience after that.
Re "you said it was called Matrix": fair, but I wouldn't send people to "matrix" / the protocol for any system with multiple implementations. I'd send them a link to one of the user-friendly apps (i.e. Element). Similarly, you wouldn't tell someone to join XMPP, you'd send them to the Google Hangouts or MSN Messenger or Playstation apps.
Re "you said it was called Matrix": fair, but I wouldn't send people to "matrix" / the protocol for any system with multiple implementations. I'd send them a link to one of the user-friendly apps (i.e. Element). Similarly, you wouldn't tell someone to join XMPP, you'd send them to the Google Hangouts or MSN Messenger or Playstation apps.