That isn't a Perl problem. Your web server isn't configured to do what you want it to do. It hasn't been told to treat the file as a CGI script.

If you want to treat all .cgi files in a directory and subdirectories as CGI scripts:

<Directory /some/dir/htdocs/>
   Options +ExecCGI
   AddHandler cgi-script .cgi
</Directory>
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If you want to treat all files in a directory and subdirectories as CGI scripts:

<Directory /some/dir/cgi-bin/>
   Options +ExecCGI
   SetHandler cgi-script
</Directory>
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There's also ScriptAlias.

Even though you're just learning cgi, its a good time to start thinking about security. The first thing you should do is be sure that your script directory is outside of your html document tree, and use ScriptAlias as mentioned by ikegami. You might also want to read this node on cgi security.

# this
/path/to/apache
           |
           +---/cgi-bin
           |
           +---/htdocs
      
# not this      
/path/to/apache
           |
           +---/htdocs      
                  |
                  +---/cgi-bin
      
# add to httpd.conf
ScriptAlias /cgi-bin/ "/path/to/apache/cgi-bin/"
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i recommend that you read Chapter 12: Introduction to CGI (in PDF format) from the freely available book Beginning Perl.