<apex:page controller="Controller">
<apex:pageBlock >
	<apex:form >
		<apex:inputText value="{!texto}"/>
		
		
		<apex:outputPanel id="panel" >
			LA RESPUESTA ES: 
			{!respuesta}
		</apex:outputPanel>
		<br></br>
		<apex:commandButton value="Consultar" action="{!ejecutaMetodo}" rerender="panel"/>
			
	</apex:form>
	
</apex:pageBlock>
</apex:page>

global class Controller {
    
    String texto='';
    String respuesta='';
    
    public String getTexto()
    {
        return this.texto;
    }
    
    public String getRespuesta()
    {
        return this.respuesta;
    }
    
    public void setTexto(String text)
    {
        this.texto=text;
    }
    
    public PageReference ejecutaMetodo()
    {       
    	      
         prueba.SalesforceWSPort testService=new prueba.SalesforceWSPort();
         this.respuesta=testService.testWebService(this.texto);
         return null;
    }

}

   This is the wsdl:

<?xml version="1.0" encoding="UTF-8"?>
<wsdl:definitions targetNamespace="http://SalesforceWS" xmlns:apachesoap="http://xml.apache.org/xml-soap" xmlns:impl="http://SalesforceWS" xmlns:intf="http://SalesforceWS" xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/" xmlns:wsdlsoap="http://schemas.xmlsoap.org/wsdl/soap/" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
	<wsdl:types>
		<schema elementFormDefault="qualified" targetNamespace="http://SalesforceWS" xmlns="http://www.w3.org/2001/XMLSchema">
			<element name="testWebService">
				<complexType>
					<sequence>
						<element name="testString" type="xsd:string"/>
					</sequence>
				</complexType>
			</element>
			<element name="testWebServiceReturn">
				<complexType>
					<sequence>
						<element name="testWebServiceReturn" type="xsd:string"/>
					</sequence>
				</complexType>
			</element>
		</schema>
	</wsdl:types>

   <wsdl:message name="testWebServiceReturn">
		<wsdl:part element="impl:testWebServiceReturn" name="parameters"/>
   </wsdl:message>
   <wsdl:message name="testWebServiceRequest">
      <wsdl:part element="impl:testWebService" name="parameters"/>
   </wsdl:message>

   
   <wsdl:portType name="SalesforceWSPort">

		<wsdl:operation name="testWebService">
			<wsdl:input message="impl:testWebServiceRequest" name="testWebServiceRequest"/>
			<wsdl:output message="impl:testWebServiceReturn" name="testWebServiceReturn"/>
		</wsdl:operation>

   </wsdl:portType>

   <wsdl:binding name="SalesforceWSSoapBinding" type="impl:SalesforceWSPort">
		<wsdlsoap:binding style="document" transport="http://schemas.xmlsoap.org/soap/http"/>
		
		<wsdl:operation name="testWebService">
			<wsdlsoap:operation soapAction=""/>
			<wsdl:input name="testWebServiceRequest">
				<wsdlsoap:body use="literal"/>
			</wsdl:input>
			
			<wsdl:output name="testWebServiceReturn">
				<wsdlsoap:body use="literal"/>
			</wsdl:output>
		</wsdl:operation>

   </wsdl:binding>

   
   <wsdl:service name="SalesforceWSService">

      <wsdl:port binding="impl:SalesforceWSSoapBinding" name="SalesforceWSPort">

         <wsdlsoap:address location="endpoint...."/>

      </wsdl:port>

   </wsdl:service>

</wsdl:definitions>

 this is the generatedCode:

//Generated by wsdl2apex

public class prueba {
    public class testWebService_element {
        public String testString;
        private String[] testString_type_info = new String[]{'testString','http://www.w3.org/2001/XMLSchema','string','1','1','false'};
        private String[] apex_schema_type_info = new String[]{'http://SalesforceWS','true','false'};
        private String[] field_order_type_info = new String[]{'testString'};
    }
    public class SalesforceWSPort {
        public String endpoint_x = 'myendpoint';
        public Map<String,String> inputHttpHeaders_x;
        public Map<String,String> outputHttpHeaders_x;
        public String clientCertName_x;
        public String clientCert_x;
        public String clientCertPasswd_x;
        public Integer timeout_x;
        private String[] ns_map_type_info = new String[]{'http://SalesforceWS', 'prueba'};
        public String testWebService(String testString) {
            prueba.testWebService_element request_x = new prueba.testWebService_element();
            prueba.testWebServiceReturn_element response_x;
            request_x.testString = testString;
            Map<String, prueba.testWebServiceReturn_element> response_map_x = new Map<String, prueba.testWebServiceReturn_element>();
            response_map_x.put('response_x', response_x);
            WebServiceCallout.invoke(
              this,
              request_x,
              response_map_x,
              new String[]{endpoint_x,
              '',
              'http://SalesforceWS',
              'testWebService',
              'http://SalesforceWS',
              'testWebServiceReturn',
              'prueba.testWebServiceReturn_element'}
            );
            response_x = response_map_x.get('response_x');
            return response_x.testWebServiceReturn;
        }
    }
    public class testWebServiceReturn_element {
        public String testWebServiceReturn;
        private String[] testWebServiceReturn_type_info = new String[]{'testWebServiceReturn','http://www.w3.org/2001/XMLSchema','string','1','1','false'};
        private String[] apex_schema_type_info = new String[]{'http://SalesforceWS','true','false'};
        private String[] field_order_type_info = new String[]{'testWebServiceReturn'};
    }
}