Hi,
I used this https://home-assistant.io/components/dialogflow/ and this Need help with API.AI to set up Dialogflow by itself. I think I had to use https://myhome.duckdns.org/api/apiai?api_password=HA_PASSWORD instead of https://myhome.duckdns.org/api/dialogflow?api_password=HA_PASSWORD though. You can then test if Dialogflow can connect with your HA.
Then the next step is to connect Dialogflow with Google actions and for that you can have a look at https://dialogflow.com/docs/integrations/google-assistant and https://developers.google.com/actions/dialogflow/first-app
Hope that helps!