Every Modula-3 program must have a single main module. Typically, the body of the main module contains the "driver" portion of your program; for small programs, the main module may be the only module. Here is a short example:
MODULE Main;
IMPORT IO;       (* So we can print things *)
VAR name: TEXT;  (* a string variable called "name" *)
BEGIN
  IO.Put("Enter your name: ");
  name:=IO.GetLine();
  IO.Put("Your name is: " & name & "\n");
END Main.
As you may have noticed, comments are enclosed in (* *).