Programming Error

import java.util.*;
import javax.mail.*;
import javax.mail.internet.*;
public class SendMail {

public static void main(String args[]) throws Exception {

String host = "192.168.10.205";
String from = "test@localhost";
String to = "test@localhost";

// Get system properties
Properties properties = System.getProperties();

// Setup mail server
properties.setProperty("mail.smtp.host", host);

// Get the default Session object.
Session session = Session.getDefaultInstance(properties);

// Create a default MimeMessage object.
MimeMessage message = new MimeMessage(session);

// Set the RFC 822 "From" header field using the
// value of the InternetAddress.getLocalAddress method.
message.setFrom(new InternetAddress(from));

// Add the given addresses to the specified recipient type.
message.addRecipient(Message.RecipientType.TO, new InternetAddress(to));

// Set the "Subject" header field.
message.setSubject("hi..!");

// Sets the given String as this part's content,
// with a MIME type of "text/plain".
message.setText("Hi ......");

// Send message
Transport.send(message);

System.out.println("Message Send.....");
}
}

I have not understood this code can u please explain me by giving me an another example.Please Sir??
Actually I have to use java mail to send a text message to my clients so i have to use this java mail but i need to understand this code.So please explain me this code.

And when i run this code it gave me 10 errors like there is no javax.mail package.So please explain me Sir??
Thank You Sir.
Thank you sir.