Taking the text of what you said and figuring out what you want to do. It sends what you said plus a list of devices/states and a list of functions (to turn off/on, set temp, etc of devices). The LLM takes "Turn off basement lights" and turns that into "{function: "call_service", args: ['lights.on', 'entity-id-123']}" (<- Completely made up but it's something like that) that it passes back to HA along with what to say back to the user ("Lights turned off" or whatever) and HA will run the function and then do TTS to respond to you.