At the very minimum, you need to define your user name and email address, which identifies you:
[ui] username = Joe Bloggs <joe@bloggs.com>
Also in this section, you’re likely to want to define a global ignore list, so that you don’t have to configure ignored files per repository. For example:
[ui] username = Joe Bloggs <joe@bloggs.com> ignore=c:\hgignore_global.txt
So here (on Windows) I’m referencing an ignore list file I’ve created at c:\hgignore_global.txt. A pretty good start for a global ignore list might look like this:
syntax: glob *~ *.orig *.rej *.swp .#* *.obj *.o *.a *.ncb *.ilk *.exe *.dll *.lib *.manifest *.pdb *.idb *.rsp *.pch *.dep *.so *.dylib *.framework
You can obviously add more elements to that if you wish.