The house music system runs on Sonos. It's connected to Spotify, Apple Music, Sonos Radio and Pandora accounts. You've got two options to play music throughout the house -- using your own phone, and your own streaming accounts, or to just use Alexa and the house accounts:
If you want to use your own music accounts from your own phone:
If you have an iPhone, you can stream audio from your phone to the Sonos system by using AirPlay. Here are instructions from Sonos. Your phone will have to be on the house Wifi system.
You can also connect to Sonos speakers using your Spotify (or similar) music app as shown in the video above.
If you just want to play music from the house system:
To turn music on throughout the house and outside without using your own phone, just use Alexa, which is connected to a speaker in the front room.
You can say things like:
"Alexa, play Thievery Corporation on Spotify"
"Alexa, play Hotel Costes radio on Pandora"
"Alexa, turn the volume up" (or down)
You can also do other things with Alexa, like say "Alexa, set a timer for 20 minutes" etc.