We don't discuss the pros and cons of particular cloaking software packages here (see the Cloaking Forum Charter [webmasterworld.com]). However, your general questions are welcome.
There are several server-side methods that can be used such as Perl, PHP, ASP or another scripting language, or Mod_Rewrite.
Ideally, a cloaked page should not redirect the browser at all. A redirection would mean that the URL in the browser would change, which is undesirable. The URL change would indicate to the web surfer that "something funny" is going on. Also, redirects can look bad to search engine spiders. Instead of redirecting, most commercial cloaking scripts use LWP or Curl to create a HTTP request for the "landing page" and display it under the same URL as the cloaked page.
I'm the admin of a site PR 4 ... Do I have to cloak pages? if yes how many?
If you have a domain with PR 4, I wouldn't recommend putting any cloaked pages on it. Get another domain and put the cloaked pages there. If a cloaked page gets penalized, you don't want your PR 4 domain to suffer.
LWP and Curl are processes by which a scripting language such as Perl or PHP makes a request through HTTP for a file, similar to how you make a request for a web page with your web browser. In essence, the script is acting like a web browser.
I am unfamiliar with the inner workings of the Fantomaster script, but I assume it does use an HTTP request.