The next thing you have to do is open the "DevTools", short for Developer Tools. On most browsers you can simply press the function key F12 and it will bring it up for you. Other ways to open the browser developer tools is right-clicking anywhere on a page and choosing to Inspect.
On Firefox for Windows, for example, you can click the hamburger icon (the three stacked lines) on the top-right corner. Then, choose More Tools, then choose Web Developer Tools.
On (Chromium-based) Edge, click the three-dots icon on the top-right corner, choose More Tools, then Developer tools.
Safari on macOS will require you go to the Advanced tab in the Preferences window and require you mark as checked "Show Develop menu in menu bar"