Symbolic Links
 

Hey guys in the rc level i see symbolic links with S20 or K20 beside a filenames what are these....

Start-up scripts. S tells the system to start the application in question at boot time, K (=kill) tells it to leave it alone. The numbers indicate the order in which applications are started at boot time.

Under standard unix the script is placed in the directory /etc/init,d. There is no S or K in front. The second number behind S or K means only that the timeming gets OK. For example: you cannot stop tcp before nfs. Or the opposite by starting. All the thing works by ls in shellscript. That means list sequetial

If i want to add a script in the init.d and create links in the run levels is there a way of correctly doing it so that it will act normally and the script will load properly upon boot.

Most of those scipts are in shell, so have a look at a few and pick one that's close to what you want, then make your own copy.
It's usually advised that you put your stuff in
/etc/rc.local
file, or the equiv for your distro. Should be that for Centos, not sure about Ubuntu.

A tip: If you want to stop a service from starting when you enter a particular run level, change the capital S to lower case S in the relevant directory.

For example, if you don't want sendmail to start when you enter run level 2:
--Ian