Are Matrix direct messages end-to-end encrypted?

I’m new to using Matrix and currently use Element on iOS as a client. The Matrix specs page notes that there is “optional” end-to-end encryption, but I don’t see an option for that. I’m just wondering if it’s a client limitation for the moment or if it’s enabled by default, and how secure the messaging is.

I would love to learn how it works so I can possibly replace some other group chat apps with friends and family.