System.enqueueJob(new QueueableExampleOne());

public void execute(QueueableContext context)
{
    System.debug(System.LoggingLevel.ERROR,'From queueable example one');
    System.debug('This is from first queue');


    String strUsername='praveen';
    String strPwd='praveen';
    Http m_http = new Http();
    HttpRequest req = new HttpRequest();

    String content = 'username='+EncodingUtil.urlEncode(strUsername, 'UTF-8')+'&password='+EncodingUtil.urlEncode(strPwd, 'UTF-8')+'&listname='+EncodingUtil.urlEncode('PraveenKumarG', 'UTF-8');

    req.setEndpoint('http://xyz/BMEapp/API.asmx/listCreate');
    req.setHeader('Content-Type','application/x-www-form-urlencoded');
    req.setMethod('POST');
    req.setBody(content);

    httpResponse response = m_http.send(req);

    System.debug('2nd callout response=='+response.getBody());

    System.enqueueJob(new QueuableExampleTwo());
}

public class QueuableExampleTwo implements Queueable, Database.AllowsCallouts{

public void execute(QueueableContext ctxt){
    System.debug('This is from second queue');

    System.debug(System.LoggingLevel.ERROR,'From QueueableContext example two');

    System.enqueueJob(new QueuableExampleThree());
}
@future(callout =true)
public static void testexecute()
{
      String strUsername='praveen';
    String strPwd='praveen';
    Http m_http = new Http();
    HttpRequest req = new HttpRequest();

    String content = 'username='+EncodingUtil.urlEncode(strUsername, 'UTF-8')+'&password='+EncodingUtil.urlEncode(strPwd, 'UTF-8')+'&listname='+EncodingUtil.urlEncode('PraveenKumarG', 'UTF-8');

    req.setEndpoint('http://xyz/BMEapp/API.asmx/listCreate');
    req.setHeader('Content-Type','application/x-www-form-urlencoded');
    req.setMethod('POST');
    req.setBody(content);

    httpResponse response = m_http.send(req);

    System.debug(response.getBody());
}}

public void execute(QueueableContext ctxt){
    System.debug('This is from third queue');

    System.debug(System.LoggingLevel.ERROR,'From QueueableContext example two');

}
}