While Teslas have had Voice Commands for a while, they were originally quite basic. The new revamped version of Voice Commands first appeared in the release notes for 2019.40.50 (official thread and discussion thread).
Voice commands have been rebuilt to understand natural language. For this initial release, we focused on commands that minimize having to touch the screen so you can keep your eyes on the road. A few areas and examples of what you can say are:
Climate: "Set the temperature to 70", "Turn on the passenger seat heater"
Vehicle: "Adjust my right mirror", "Open the glovebox"
Navigation: "Let's go to work", "Where are the nearby supercharging stations"
Media: "Play the Beatles", "Search for Joe Rogan podcast"
Communication: "Call David Lewis", "Send a text message to Evan"
Other: "Show me the rear camera", "Open Autopilot settings"
Anonymized voice commands will be captured to further train and improve the system in future software updates.