How Do You Get to the Nice HTML Presented Installation Web Page for Craft CMS?

Problem scenario
You are trying to install Craft CMS, but when you go to the web browser, you see this:

HTTP 503 – Service Unavailable – craft\web\ServiceUnavailableHttpException
in /var/www/html/craft/vendor/craftcms/cms/src/web/Application.php
537538539540541542543544545546547548549550551552553554555       
 $actionSegs = $request->getActionSegments();
        if (isset($actionSegs[0]) && $actionSegs[0] === 'install') {
            return $this->_processActionRequest($request);
        }
    }

    // Should they be accessing the installer?
    if (!$isInstalled) {
        if (!$isCpRequest) {
            throw new ServiceUnavailableHttpException();
        }

        // Redirect to the installer if Dev Mode is enabled
        if (YII_DEBUG) {
            $url = UrlHelper::url('install');
            $this->getResponse()->redirect($url);
            $this->end();
        }

or "Invalid Configuration"

What should you do?

Solution
In the directory in the URL that you get this message, try adding this: "index.php?p=admin/install "

The URL should be something like this (but repalce "FQDNofCraftCMSServer" with the appropriate DNS server): http://FQDNofCraftCMSserver/craft/web/index.php?p=admin/install