How do I respond to a calendar invite?
Open the invite from your Agenda and choose Accept, Maybe or Decline — or just ask in plain language. Those three are the whole reply, exactly as in Google Calendar. The response is written straight to your Google Calendar and sent from your account.
There is no propose-a-new-time reply: Google Calendar's own invite reply doesn't carry one, so if the time doesn't work, decline and tell the organizer when does.
Invites that need a decision surface in your Needs Attention band. Tap the invite to open it and respond there, without opening Calendar. As with any action the assistant takes on your behalf, it's recorded in Activity.
See also: How do I act from a card? · Can it create, move, or cancel events?