Perl and Common Gateway Interface (CGI)

http://www.perl.com/pub/2000/10/begperl1.html

1. The difference between single quotes and double quotes is that single quotes mean that their contents should be takenliterally, while double quotes mean that their contents should be interpreted. For example, the character sequence \n is a newline character when it appears in a string with double quotes, but is literally the two characters, backslash and n, when it appears in single quotes. 

print "This string\nshows up on two lines."; 

print 'This string \n shows up on only one.';

2. the plus sign adds numbers and the period puts strings together.

CGI
http://en.wikipedia.org/wiki/Common_Gateway_Interface

Common Gateway Interface (CGI) is a standard method used to generate dynamic content on web pages and web applications. CGI, when implemented on a web server, provides an interface between the web server and programs that generate the web content. These programs are known as CGI scripts or simply CGIs; they are usually written in ascripting language.