If you want to run a stable version please use current_stable.ebuild
If you want to run a testing version please use current_testing.ebuild

To use the ebuild please simply copy it into your local portage tree and rename it to fpdb-version.ebuild, for example fpdb-0.20.1.ebuild or fpdb-0.20.902.ebuild.
Here's a little howto on how to utilise 3rd party ebuilds such as this one: http://www.gentoo-wiki.info/HOWTO_Installing_3rd_Party_Ebuilds