Materialized View usage in Oracle

You say "I do not have much idea about materialized views.".
Which leads me to suggest that you first get a good understanding of materialized views.
I'm not trying to ridicule you, it's just that there is a whole lot of things that can cause a MV to behave different then you would think.

In this case I wouldn't be surprised if what you're trying to do is a "fast refresh" (=wrong term, read Tom Kyte: http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:10128040625700).
And if so, again I wouldn't be surprised if you did not create a Materialized View Log on each and every underlying table of each and every view that is used for this MV.

Rob van Wijk, a dutch guy I had the pleasure to work with, has posted a couple of extensive articles about the problems he encountered with fast refresh.
They might be of help to you. They were to me.
=> http://rwijk.blogspot.com/2009/05/fast-refreshable-materialized-view.html
=> http://rwijk.blogspot.com/2009/05/fast-refreshable-materialized-view_31.html
=> http://rwijk.blogspot.com/search?q=materialized+view&updated-max=2009-06-26T01%3A08%3A00%2B02%3A00&max-results=20

Oracle Security Problems ( Block access of oracle )

From blocking it from the internet, you need to isolate your internal network from outside using firewalls so that only ports that needs to be opened are kept open and only to specific hosts within a DMZ area. Rest of your internal network should be totally isolated from outside world.

Within your network, there are many ways to protect your database. Check the oracle's website for all the products offered. Each product is designed to address specific security issues. Devise a good security practice for all your databases. Please refer to the metalink note 207959.1 which gives a very good overview on all available security features for your oracle databases.

http://www.oracle.com/us/technologies/security/security-solutions-151411.html

Installation of Oracle 10g on Red hat Linux Enterprise 5(32bit)

This site seems to have a pretty good guide...i hope it is useful

http://www.oracleflash.com/12/How-to-Install-Red-Hat-Enterprise-Linux-5.html 
http://www.oracleflash.com/18/Install-Oracle-10g-Release-2-on-RHEL-5.html