1. The easiest and most well-known method for launching Assistant is simply long-pressing the on-screen home button. The edges of the screen will flash with a white outline and Assistant will pop up from the bottom of the screen. You can immediately start speaking a command. When you do this for the first time you will be asked to opt-in and set up Assistant.
2. The second built-in method requires a little more set-up. You can use your voice to launch Assistant by saying “Ok, Google” or “Hey, Google.” This needs to be enabled and configured in the Google Assistant app.