i'm totally clueless about sth i'm interested on.
Files of php and cgi. How does it work..
How do u let visitor upload files or sort..

explaining Perl or PHP entirely in a post would be extremely long.
perhaps do a search in this forum for tutorials on the subject.
if you start on a specific project, post questions on how to do the next step if you get stuck.

Search google for php tutorials:
http://www.google.co.uk/search?q=PHP+tutorials&ie=UTF-8&hl=en&meta=

Search google for cgi tutorials:
http://www.google.co.uk/search?hl=en&ie=UTF-8&safe=off&q=CGI+tutorials&meta=

Hope that helps
Chris