Youmustinstallelixir1.4+fromelixir-lang.org,becauseDebianreposonlyhave1.3.xversion.Youwillneedtoaddaptrepotosources.list(.d)andimportGPGkey.Followinstructionshere:https://elixir-lang.org/install.html#unix-and-unix-like (See "Ubuntu or Debian 7"). This should be valid until Debian updates elixir in their repositories. Package you want is named `elixir`, so install it using `apt install elixir`
Bydefault,itlistensonport4000(TCP),soyoucanaccessitonhttp://localhost:4000/ (if you are on the same machine). In case of an error it will restart automatically.