I only know the basics of it, but create a .html page, for example, with some JS in it. A simple example would be
Now, open Chrome, click View > Developer > Developer Tools, and a window opens at the bottom of the browser. Click the Console tab, then refresh the page. You will see the output of the script at the in the Console window. (There are instructions for the Mac version of Chrome, but I assume it's similar on Windoze.)
var name = "Jack";
console.log("My name is " + name);
You can type instructions in the Console, too, and thus interact with the browser.
This is a great video that shows what you can do with Chrome dev tools: