If Siri wasn’t activated while setting up your iPad, you can activate it by opening Settings, pressing Siri & Search and then turning it on. You’ll want to ensure Press Top Button for Siri, or Press Home for Siri, is toggled on.
Siri is your personal assistant, and can be used to control certain functions on the phone by using voice commands. To access Siri, press and hold the Top or Home button for a few seconds until the Siri interface appears, and then start speaking.