How to make Debian package install dependencies?

Question

I want to make a simple Debian package to install a simple tool that depends on Qt4 libs.

In control file I have defined that it depends on Qt4 libs however, by the time

Answer 1

If you're creating the Debian package, you specify its dependencies in the debian/ directory control files; I believe debian/control takes Depends: directives for that purpose.

I don't know the details too clearly, myself, but there are instructions at http://www.debian.org/doc/manuals/maint-guide/ ; in particular, http://www.debian.org/doc/manuals/maint-guide/dreq.en.html#control seems to be the right place to start looking.