i am creating Email Service class  my requirement is when task status is completed then email will sent to assign contact persion emai id...so.....i am new to Email service concept.please help me...here is my code

global class emailservice implements Messaging.InboundEmailHandler {

global Messaging.InboundEmailResult handleInboundEmail(Messaging.inboundEmail email,
                                                  Messaging.InboundEnvelope env){

// Create an inboundEmailResult object for returning
// the result of the Force.com Email Service
Messaging.InboundEmailResult result = new Messaging.InboundEmailResult();

     task te=[select id,status,whoid from task limit 1];
     Contact c=[select id,lastname,Account.Name,email  from contact where id=:te.whoid];
     String myPlainText = 'I spoke with '+c.lastname+ 'today from '+ '  '+c.account.name +'  '+'about the latest proposal.';

// Add the email plain text into the local variable

try
{
      myPlainText = email.plainTextBody.substring(0, email.plainTextBody.indexOf('<stop>'));
}
catch (System.StringException e)
{
     myPlainText = email.plainTextBody;
     System.debug('No <stop> in email: ' + e);
}

// Set the result to true, no need to send an email back to the user
// with an error message
  if(te.status=='completed')
  result.success = true;
  // Return the result for the Force.com Email Service
  return result;
}
}