From The Debian GNU/Linux FAQ, version CVS, 14 February 2003
6.14 How do I build binary packages from a source package?
You will need all of foo_.dsc, foo_.tar.gz and foo_*.diff.gz to compile the source (note: there is no .diff.gz for some packages that are native to Debian).
Once you have them (How do I install a source package?, Section 6.13), if you have the dpkg-dev package installed, the following command:
dpkg-source -x foo_version-revision.dsc
will extract the package into a directory called foo-version.
If you want just to compile the package, you may cd into foo-version directory and issue the command
dpkg-buildpackage -rfakeroot -b
to build the package (note that this also requires the fakeroot package), and then
dpkg -i ../foo_version-revision_arch.deb
to install the newly-built package(s).