-module(main).
-export([hello/0]).

hello() ->
    io:format("Hello, world!~n").

Compile and run in the Erlang shell:

c(main).
main:hello().

This defines a tiny Erlang module and a function that prints one line to the shell.

Variables are single-assignment and start with an uppercase letter.

Name = "Dan",
Count = 1,
Active = true.

These are single-assignment bindings. Once a variable has a value in Erlang, you do not mutate it in place.

greet({user, Name}) ->
    io:format("Hello, ~s!~n", [Name]).

This matches a tuple argument and pulls the name out directly in the function head.