There are lots of topics about this here 
Just search the forum for keywords that you think are relevant.
For example :- Chromecast / Google Home - automatic start playing a stream when motion is detected in a room
But reading this will help you…
Take away information is that Sonos, ChromeCast, onboard audio & WebAudio are all potential AudioSinks.
You can push URLs into most AudioSinks, as well as TTS commands.
And if you want to host sound files on your server, they are best placed in the sounds/ folder.
On Linux, that is normally…
/etc/openhab2/sounds