1.
Create a project in Google Cloud Platform Console using your google account.
If you have an existing project, you can choose it from the dropdown or else create a new project.
2.
Enable the Maps Javascript API from the APIs page.
Enable the Directions API if you want to use the directions services methods for showing routes.
Enable the Places API if you want to use the places services methods..
Enable the Elevation API if you want to use the elevation service.
Enable the Distance Matrix API if you want to use the distance matrix service.
3. To get your API Key create a credentials at Credentials page.
Once your done, your can now copy your API Key and start building your app.