Not that I am aware of (the man page to help understand startup dir) however you might find some discussion on sysVinit around the board and on google.com/linux
As for "create file Test with code" and just place it in that directory, not likely. You probably have runlevel directories though (rc.3 or rc3.d) that correspond to your current runlevel (to find out check /etc/inittab and look for id:3:default or something similar, might be 5) and you could do what you are wanting there. Make sure it's executable though.
What I'd suggest is finding an rc.local file and using that instead. Almost every distro I've used has one, run a search:
find / rc.local
Inside there you can do what you are wanting, this file is exactly for what you are looking to do.