In order to send emails you should have a valid SMTP server for relaying the emails, that your application sends.
Also you should create a valid account for receiving emails.
Include the namespace System.Net.Mail in order to make use of the below function. Note that my comments are inlined
public void SendEmail(string smtpHost, string subject, string body, string fromId, string toId)
string replyToId = "firstname.lastname@example.org";
MailMessage message = new MailMessage();
message.Subject = subject;
message.Body = body;
//Set this in order to represent the email body as a HTML text and format accordingly
message.IsBodyHtml = true;
message.From = new MailAddress(fromId);
//This will the id which will be in the To list, when user clicks on reply in his mail box.
//so properly configure it
message.ReplyTo = new MailAddress(replyToId);
SmtpClient client = new SmtpClient(smtpHost);