When packaging Ubuntu packages, there's always these funny .dir and .install files around. I suppose their purpose is to somehow indicate what files are to be installed, but I'm not so sure about what the the format of those files is, nor what the consequences are when they are omitted.
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(/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:
Likewise goes for debian/dirs and debian/packagename.dirs which instead creates empty directories:
It's normally unnecessary unless you specifically need an empty directory or if there is a problem with the source Makefile...