[preethisingh]

what's is the use of 'require' and what does this mean?

[ishadalwadi]

require() reads a file containing Perl code and compiles it. Before attempting to load the file it looks up the argument in %INC to see whether it has already been loaded. If it has, require() just returns without doing a thing. Otherwise an attempt will be made to load and compile the file.
require() has to find the file it has to load. If the argument is a full path to the file, it just tries to read it. For example:
require "/home/httpd/perl/mylibs.pl";

If the path is relative, require() will attempt to search for the file in all the directories listed in @INC. For example:
require "mylibs.pl";