An API key can be gotten by visiting https://developers.google.com/places/web-service/get-api-key, scrolling to the Get an API key section, and clicking the GET A KEY button:

Upon clicking the button, you will be presented with a modal from which you can select or create a project to be integrated with the Google Places API Web Service. Click on the dropdown and select Create a new project. You will be requested to provide a project name. Input Place Reviewer as the project name:

After providing a project name, click NEXT to proceed. Your project will be set up for use with the API and you will be presented with an API key to use!

Now that we have an API key, let's have a look at how to use it.