Thanks to running rails new in Section 1.2.3 and bundle install in Section 1.2.4, we already have an application we can run—but how? Happily, Rails comes with a command-line program, or script, that runs a local web server, visible only from your development machine:13

       Figure 1.3 The default Rails page.

(If your system complains about the lack of a JavaScript runtime, visit the execjs page at GitHub for a list of possibilities. I particularly recommend installing Node.js.) This tells us that the application is running on port number 300014 at the address 0.0.0.0. This address tells the computer to listen on every available IP address configured on that specific machine; in particular, we can view the application using the special address 127.0.0.1, which is also known as localhost. We can see the result of visiting http://localhost:3000/ in Figure 1.3.

       To see information about our first application, click on the link ‘‘About your application’s environment.’’ The result is shown in Figure 1.4. (Figure 1.4 represents the environment on my machine when I made the screenshot; your results may differ.)