Generally speaking you would utilize Home/Away routines. If you have the "Nest Thermostat" (released 2020) it is all schedule based, not learning, and is fairly easy. Setup presence sensing in Google Home: Google Home -> (thermostat-name) -> Settings (gear icon) -> Presence Sensing. Configure the thermostat to use the Home/Away routines and when home set temperature to on using the schedule, and when away set the temperature to "Eco". Then adjust Eco to be the temp you want when you are away.
To start with, I recommend only enable your phone(s) for presence sensing and no other devices - though you can include the thermostat sensor. Every person's phone in the household should participate in presence sensing. People with more than one phone should generally only enable one. It will use the phone's location services to determine if a particular phone is nearby or not. When all phones are no longer nearby the Away routine (Google Home) will start and the thermostat is set to Eco. When one phone is nearby the Home routine will start setting the temp to your schedule.
Some helpful info:
https://support.google.com/googlenest/answer/10071810?hl=en
https://support.google.com/googlenest/answer/10000312?hl=en
