Use the Gemini app 
Use any of these shortcuts:
Say a command or ask a question.
Ask about your current screen by saying “What am I looking at?”
To learn about changing settings for 

Tap your profile icon 

If your phone isn't recognizing “Hey, Google” commands:
Check Battery saver: When on, voice triggers (“Hey Google”) are disabled. Use a different shortcut to start voice commands, or turn off Battery saver.