DEBIAN which contains the postinst,
control
and the copyright
file.
Correct information about creating Debian packages can be found here
The task of the postinst script is it to "install" the actual
installation script. You could, in theory, run everything from the postinst, BUT it does not work reliably. I do not know why. For this reason we have the install.sh script in the etc/init.d folder
Here is a bit of good info I found about Debian packages on ubuntu-mobile
'apt-get source PACKAGE' downloads a source package and unpacks it into a subdirectory of the current directory; 'sudo apt-get build-dep PACKAGE' downloads and installs build-dependencies of a source package; 'debuild -b' (from the devscripts package; install fakeroot too) in the unpacked source tree builds binary packages. The pbuilder package can help to automate much of this in a clean chroot environment.
etc which has a folder inside called init.d which contains the file install.sh
home which contains the user home directory you want to install