To find out the port of the proxy server, you just need to use any browser (Yandex Browser, Opera, Google Chrome). Then you need to follow the algorithm:

Start the browser. Go to "Settings". In the search box enter the query "proxy". Click on "Proxy settings". In the window that opens, select "Network settings". This will open a tab with the IP address and port of the proxy server.

It means organizing a connection through several VPN-servers at once. It is used to protect confidential data as much as possible or to hide one's real IP address. This principle of connection is used, for example, in the TOR-browser. That is, when all traffic is sent immediately through a chain of proxy servers.

To find an element by its HTML code in Selenium, you can use the ExecuteScript method to execute JavaScript code that returns the element corresponding to the provided HTML code. Here's an example of how to do this using C#:

Install the required NuGet packages:

Install-Package OpenQA.Selenium.Chrome.WebDriver -Version 3.141.0
Install-Package OpenQA.Selenium.Support.UI -Version 3.141.0

Create a method to find an element by its HTML code:

using OpenQA.Selenium;
using OpenQA.Selenium.Support.UI;
using System;
using System.Text.RegularExpressions;

public static IWebElement FindElementByHtml(this IWebDriver driver, string htmlCode)
{
    // Execute JavaScript to create a new element with the provided HTML code
    var script = $@"var div = document.createElement('div'); div.innerHTML = arguments[0]; document.body.appendChild(div); return div.children[0];";
    var element = (IWebElement)driver.ExecuteScript(script, htmlCode);

    // Remove the created element from the DOM
    driver.ExecuteScript("document.body.removeChild(document.body.children[document.body.children.length - 1]);");

    return element;
}

Use the FindElementByHtml method in your test code:

using OpenQA.Selenium;
using System;

namespace SeleniumFindElementByHtmlExample
{
    class Program
    {
        static void Main(string[] args)
        {
            // Set up the WebDriver
            IWebDriver driver = new ChromeDriver();
            driver.Manage().Window.Maximize();

            // Navigate to the target web page
            driver.Navigate().GoToUrl("https://www.example.com");

            // Find an element by its HTML code
            IWebElement element = driver.FindElementByHtml(@"
                

                    
Example Heading
                    
Example paragraph text.
                
");

            // Perform any additional actions as needed

            // Close the browser
            driver.Quit();
        }
    }
}

In this example, we first create a method called FindElementByHtml that takes an IWebDriver instance and a string containing the HTML code as input. Inside the method, we use the ExecuteScript method to execute JavaScript code that creates a new element with the provided HTML code, appends it to the document body, and returns the created element.

We then remove the created element from the DOM using another ExecuteScript call. The method returns the created element as an IWebElement.

In the test code, we set up the WebDriver, navigate to the target web page, and use the FindElementByHtml method to find an element by its HTML code. After finding the element, you can perform any additional actions as needed.

Remember to replace the HTML code in the FindElementByHtml method call with the actual HTML code you want to use.

This depends directly on how the proxy server works. Some of them do not require any authorization at all, others require username and password for access, and others require you to view ads and so on. Which option will be used depends directly on the service that provides access to the proxy server.

Rotary proxies are proxies that cyclically change their real IP address. This is used to make it harder to track their location. The port usually changes as well. How this happens depends on the software used on the proxy server.