For your own project, just add the following text-notice to the header/first section of each of your source-files, commented out in whatever way your language uses:
----------------following is the notice-----------------
* Your Project Name - -you slogan-
* Copyright (C) 2007 - 2007 Your Name
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
the "2007 - 2007" needs to be adjusted to "year when you gave it the license in the first place" - "current year".
Then put the file gpl.txt into the source-folder or a docs folder: http://www.gnu.org/licenses/gpl.txt
If you are developing together with other people, you need their permission to put the project under the GPL.
Just for additional Info, I found this license comparision paper by sun: http://mediacast.sun.com/share/webmink/SunLicensingWhitePaper042006.pdf
And comments to it: http://blogs.sun.com/webmink/entry/open_source_licensing_paper#comments
It does look nice, but it misses one point:
GPL is trust: Contributors can trust, that their contributions will keep helping the community, and that the software they contribute to will keep being accessible for the community.
(That's why I decided some years ago to only support GPL projects. My contributions to one semi-closed project got lost, because the project wasn't free and the developer just decided not to offer them anymore, and I could only watch hundreds of hours of work disappear, and that hurt.)
PS: If anything's missing, please write a comment!
The European Copyright directive threatens online communication in Europe.
But thanks to massive shared action earlier this year, the European parliament can still prevent the problems. For each of the articles there are proposals which fix them. The parliamentarians (MEPs) just have to vote for them. And since they are under massive pressure from large media companies, that went as far as defaming those who took action as fake people, the MEPs need to hear your voice to know that your are real.
If you care about the future of the Internet in the EU, please Call your MEPs.