So you have a script of your own that you want to run at bootup, each time
you boot up. This will tell you how to do that.
Write a script. put it in the /etc/init.d/ directory.
Lets say you called it FOO. You then run

You also have to make the file you created, FOO, executable, using

You can check out man update-rc.d for more information. It is a Debian
utility to install scripts. The option defaults puts a link to start FOO in
run levels 2, 3, 4 and 5. (and puts a link to stop FOO into 0, 1 and 6.)

Also, to know which runlevel you are in, use the runlevel command.

If you want to remove the script, just run: