To use telnet to retrieve HTTP protocol, you can follow the steps below:

1. Open your command prompt or terminal.

2. Type "telnet" followed by the domain name or IP address of the web server you want to connect to. For example, "telnet www.example.com 80" connects to the web server "www.example.com" on port 80, which is the default port for HTTP.

3. Press Enter to initiate the telnet connection.

4. Once connected, you can manually send an HTTP request by typing it in. The HTTP request consists of the following parts:

   - Request line: This includes the HTTP method (e.g., GET, POST), the path to the resource, and the HTTP version.

   - Headers: These provide additional information about the request, such as the host, user-agent, and any cookies.

   - Blank line: This signifies the end of the headers.

   - Optional message body: This is typically used with POST requests to send data to the server.

5. After typing the HTTP request, press Enter twice to send it to the server.

6. You should then receive a response from the server, which includes an HTTP status code, headers, and the response body (if applicable).

Here's an example of a simple HTTP GET request sent using telnet:

```

GET /index.html HTTP/1.1

Host: www.example.com

User-Agent: Mozilla/5.0

Accept: text/html

```

After sending this request, the server will respond with the corresponding HTTP response, which you can view in the telnet session.

It's important to note that using telnet for HTTP requests is a manual and low-level approach and is typically used for troubleshooting or educational purposes. In practice, it's more common to use specialized tools or programming libraries to interact with web servers and retrieve HTTP resources.

In conclusion, using telnet to retrieve HTTP protocol involves establishing a connection to the web server and manually crafting and sending HTTP requests. While it provides a basic understanding of how HTTP works, it's not the most efficient or practical method for interacting with web servers in real-world scenarios.