A CGI program in Perl generally prints a header and then simply prints the HTML to STDOUT, as has been noted. A simple (untested) "Hello World!" example follows:

use strict;
use CGI;

print header();
print start_html();
print h1("Hello, World!");
print end_html();
[download]

As noted, no explicit file handle is needed, since your script is simply printing to STDOUT.

Please do follow the advice you've been given and read up on CGI.

Note also that your script needs to be executable by the user under which your webserver runs. This generally means you need to chmod your script to 755 if running under some form of Unix.