Yes, to first connect to someone you share a qr code with them or send them a link. The medium in which you share the link does not have to be secure, it is only to make the first connection between the two of you.

Here's a high-level overview explaining how it is possible that there are no user identifiers. Basically, with each contact you agree on different servers which relay your messages. You get separate communication tunnels for every contact. And these tunnels can be replaced by other tunnels at any time.