The following piece of code will let you send email using the Google server. Just replace the network credentials with your Google user name and password.

//Short Method
try
{
    SmtpClient smtp = new SmtpClient("smtp.gmail.com", 587);
    smtp.UseDefaultCredentials = false;
    smtp.Credentials = new NetworkCredential("username", "password");
    smtp.EnableSsl = true;
    smtp.Send("sender@gamil.com", "receiver", "subject", "Email Body");
}
catch(Exception ex)
{
    Console.WriteLine(ex.Message);
}

//Detailed Method
try
{
    MailAddress mailfrom = new MailAddress("sender@gmail.com");
    MailAddress mailto = new MailAddress("receiver@abc.com");
    MailMessage newmsg = new MailMessage(mailfrom, mailto);

    newmsg.Subject = "Subject of Email";
    newmsg.Body = "Body(message) of email";

    //For File Attachment, more file can also be attached
    Attachment att = new Attachment("C:\\...file path");
    newmsg.Attachments.Add(att);

    SmtpClient smtp = new SmtpClient("smtp.gmail.com", 587);
    smtp.UseDefaultCredentials = false;
    smtp.Credentials = new NetworkCredential("username","password");
    smtp.EnableSsl = true;
    smtp.Send(newmsg);    
} 
catch(Exception ex)
{
    Console.WriteLine(ex.Message);
}

Note: Before providing the credentials, you need to set UserDefaultCredentials to false. The above mentioned settings are for Gmail, but you can also use other SMTP servers like Yahoo!