diff --git a/README.md b/README.md
index ab4be06..271eff7 100644
--- a/README.md
+++ b/README.md
@@ -1,2 +1,91 @@
 # csoap
 A lightweight C++ SOAP client library.
+
+## Usage
+
+Firstly, please install SoapUI if you don't have it. We need SoapUI to help us parse the WSDL and generate sample requests for each web service API. The open source version is good enough.
+
+Take the calculator web service provided by ParaSoft as an example. Download the WSDL from http://ws1.parasoft.com/glue/calculator.wsdl, create a SOAP project within SoapUI (remember to check "Create sample requests for all operations?"), you will see the sample request for "add" operation as the following:
+```xml
+<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:cal="http://www.parasoft.com/wsdl/calculator/">
+<soapenv:Header/>
+<soapenv:Body>
+   <cal:add>
+      <cal:x>1</cal:x>
+      <cal:y>2</cal:y>
+   </cal:add>
+</soapenv:Body>
+</soapenv:Envelope>
+```
+
+In order to call the "add" operation, we have to send a HTTP request with the above SOAP envelope as the content. Let's see how to do this with csoap.
+
+```cpp
+bool Call() {
+  std::string operation = "add";
+
+  // Create a SOAP request which abstracts the SOAP envelope.
+  csoap::SoapRequest soap_request(operation);
+
+  // Set the service namespace.
+  csoap::Namespace service_ns = { "cal", "http://www.parasoft.com/wsdl/calculator/" };
+  soap_request.set_service_ns(service_ns);
+
+  // Add parameters for the operation.
+  soap_request.AddParameter("x", "1.0");
+  soap_request.AddParameter("y", "2.0");
+
+  // Generate the XML string for the SOAP envelope.
+  std::string http_request_body;
+  soap_request.ToXmlString(&http_request_body);
+
+  // Create a HTTP request.
+  csoap::HttpRequest http_request(csoap::kHttpV11);
+
+  // Set the HTTP headers.
+  http_request.set_url("/glue/calculator");
+  http_request.set_content_length(http_request_body.size());
+  http_request.set_host("ws1.parasoft.com", "");
+  http_request.set_soap_action(operation);
+
+  // Send the HTTP request and get the HTTP response.
+
+  csoap::HttpResponse http_response;
+
+  csoap::HttpClient http_client;
+  csoap::ErrorCode ec = http_client.SendRequest(http_request,
+                                                http_request_body,
+                                                &http_response);
+
+  // Error handling.
+  if (ec != csoap::kNoError) {
+    std::cerr << csoap::GetErrorMessage(ec) << std::endl;
+    return false;
+  }
+
+  // Parse the SOAP response.
+  std::string result;
+  csoap::SoapResponse soap_response;
+  if (!soap_response.Parse(http_response.content(), "addResponse", "Result", &result)) {
+    return false;
+  }
+
+  std::cout << result << std::endl;
+
+  return true;
+}
+```
+
+It's not that complicated. But you can't code like this for each operation. You have to do some encapsulation, make a general function, add a base class, etc. Check the "demo" folder for the detailed example.
+
+## Limitations
+
+- Only support HTTP 1.1.
+- Only support int, double, bool and string parameters.
+- Only support UTF-8 content.
+
+## Dependencies
+
+- The TCP socket client is based on Boost.Asio.
+- The XML parsing is based on TinyXml or PugiXml, a macro CSOAP_USE_TINYXML controls which one to use.
+- Build system is CMake, but it should be easy to add into your project.
diff --git a/src/demo/calculator.h b/src/demo/calculator.h
index 2353b02..4106846 100644
--- a/src/demo/calculator.h
+++ b/src/demo/calculator.h
@@ -2,7 +2,7 @@
 #define DEMO_CALCULATOR_H_
 
 // Wrapper of calculator.wsdl.
-// See http://service-repository.com/service/overview/877027757
+// See http://ws1.parasoft.com/glue/calculator.wsdl
 
 #include <string>
 #include "csoap/common.h"