Siri is software for the HomePod, iPhone, and macOS from Apple that provides the user with a personal assistant that performs various tasks based on the user's voice commands. It can answer questions, schedule meetings, send messages, and do other things that are helpful to the user. As an example, the user can say a command such as "Wake me up at 6:30 a.m.," and Siri sets an alarm to wake up the user at that time.
To use Siri on an iPhone, press and hold the home button for two or three seconds, then release. Siri will visually and audibly activate, letting you know it's ready to accept voice commands.