Postman REST Client can be installed in two different ways, but both require Google Chrome to be installed and running on your system. The easiest way to install the application is by visiting the chrome web store at https://chrome.google.com/webstore/category/apps.

Perform a search for Postman REST Client, and multiple results will be returned. There is the regular Postman REST Client that runs as an application built into your browser, and then a separate Postman REST Client (packaged app) that runs as a standalone application on your system in its own dedicated window. Go ahead and install your preference. If you install the application as the standalone packaged app, an icon to launch it will be added to your dock or task bar. If you install it as a regular browser app, you can launch it by opening a new tab in Google Chrome, going to Apps, and finding the Postman REST Client icon.

After you've installed and launched the app, you should be presented with an output similar to the following screenshot: