howto add patches?

[GCS <gcs@lsc.hu>]

Hi all,

 I would like to ask how can I add a patch to an existing package? I
have created debian/patches, placed my patch there. Adding a 'patch -p1 <
..' seems to be ok for the first time. But second time, it fails, as the
source is already patched. How can I use a stamp file maybe showing it
is already patched, and skip it? Also, I have noticed dbs, but I have no
idea at all, how should I use it. It seems I have to reorganize the
package, put the tarball into the package instead of the source
directly, and do some magic. Any docs on this subject?

Thanks,
GCS