A Java servlet is a Java class that dynamically generates content that is served over the web using HTTP. When a client, such as a web browser, sends a request to the server, the request is processed by the web server and then forwarded to the appropriate servlet to generate the response.

Here's a step-by-step explanation of how a servlet works:

1. The client sends a request to the web server, usually by entering a URL in their web browser.

2. The web server receives the request and determines which servlet should handle it based on the URL.

3. The web server creates a new thread to handle the request and passes the request and response objects to the servlet.

4. The servlet uses the request object to extract any parameters, cookies, or other information from the client's request.

5. The servlet generates the response, usually by dynamically generating HTML or other content based on the information it received from the client.

6. The servlet uses the response object to send the generated content back to the web server.

7. The web server sends the response back to the client, which displays the content in the web browser.

This process can be repeated many times for different clients, each of which can receive a unique response based on their individual requests.

It's worth noting that servlets are not tied to a specific web server or operating system. They can run on any server that supports the Java Servlet API, and they can be deployed on a variety of operating systems, including Windows, Linux, and macOS.