Go to your central repository, not your working copy. There, change to the hooks directory:
cp post-receive.sample post-receive
If your repo is not a bare repository, you have to change to .git/hooks to do this. The post-receive-email script can be found under contrib/hooks/ in the git documentation (e.g. in /usr/share/doc/git/contrib/hooks on most Linux distributions).
Now configure the email hook:
git config hooks.mailinglist "firstname.lastname@example.org, email@example.com"
git config hooks.envelopesender firstname.lastname@example.org
git config hooks.emailprefix "New commit: "
Also you should give your project a name: