Purpose of .dir, .install files in packages

debian/install and debian/packagename.install files both have the same purpose, the latter being used in case you build multiple binary packages from the same source (so you need to distinguish which files go into which resulting package).

If the source Makefile (and other install system) already takes care of installing for you, they are generally not needed, (extra) files that aren't installed otherwise can be installed by these.

The syntax is simply:

path/sourcedir/file path/installdir
# for example
data/foo.jpg usr/share/packagename

See http://www.debian.org/doc/manuals/maint-guide/dother.en.html#install

--

Likewise goes for debian/dirs and debian/packagename.dirs which instead creates empty directories:

path/installdir

It's normally unnecessary unless you specifically need an empty directory or if there is a problem with the source Makefile...

See http://www.debian.org/doc/manuals/maint-guide/dother.en.html#dirs