I see wiki pages http://wiki.ros.org/audio_common and http://wiki.ros.org/sound_play . The second link has instructions on how to set it up, and examples for doing text-to-speech from the command line and from a ros topic. It appears clearly explained to me.

Of course, this package assumes that your motherboard has sound hardware, at least one audio speaker is hooked up, and that the linux audio service is working (pulseaudio I imagine?)