Google provides a developer tool to build Google Home actions / Google Assistant applications. The underlying NLU on the Google Assistant is called Dialogflow (previously known as api.ai, which was acquired by Google in 2016).
In this tutorial, I will focus on the Dialogflow tool available for building conversational applications.
Create your account or log in: To start building actions, you will need to open an account on Google Actions. Visit https://console.actions.google.com/ and use your Google account to log in. If needed, create a new free account.
Add/import your project: To start a new project or import a project you have built separately, click on the large square box.
Name your project: Name your project and decide on the location. Once you have more than one project, you will have a gallery of projects that you can further build and manage. Pick a name that is relevant for the project, so it will be easy to follow up on. When done, click on CREATE...