How to create contact form in php with validation and email function?

<?php
if($_POST['cmdsubmit']=='Submit'){
$name=$_POST['name'];
$fromemail=$_POST['email'];
$subject=$_POST['subject'];
$message=$_POST['message'];
$today = date("D M j G:i:s");  
$msgSubject="Contact Us....";
$headers  = "MIME-Version: 1.0\r\n";
$headers .= "Content-type: text/html; charset=iso-8859-1\r\n";
$headers .= "From: ".$fromemail."<".$fromname.">\n";
$message='
<table width="500" cellpadding="2" cellspacing="10" bgcolor="#ffffff" style="font-family:arial;font-size:11px">
<tr><td><b>Enquiry</b></td></tr>
<tr><td colspan=4>Name:</td><td  >'.$name.'</td></tr>
<tr><td colspan=4>Email:</td><td >'.$fromemail.'</td></tr>
<tr><td colspan=4>Subject:</td><td >'.$subject.'</td></tr>
<tr><td colspan=4>Mesage:</td><td  width =300>'.$message.'</td></tr>
<tr><td colspan=4>Send time : </td><td >'.$today.'</td></tr>
</table> <br><br> By <br>';
mail('phpcodeblog.gmail.com',$msgSubject,$message,$headers);
$Sentmsg="Mail Has Been Sent";
}
?>
<script type="text/javascript" language="JavaScript">

function trim(s) {
  while (s.substring(0,1) == ' ') {
    s = s.substring(1,s.length);
  }
  while (s.substring(s.length-1,s.length) == ' ') {
    s = s.substring(0,s.length-1);
  }
  return s;
}


function isValid(){
  var fobj = document.forms['frmmail'];
  var errors = '';

  if (trim(fobj.elements['name'].value).length == 0) errors += 'Name cannot be empty!\n';
  if (trim(fobj.elements['email'].value).length == 0) errors += 'Email cannot be empty!\n';
   if (trim(fobj.elements['subject'].value).length == 0) errors += 'subject cannot be empty!\n';
  if (trim(fobj.elements['message'].value).length == 0) errors += 'message cannot be empty!\n';
  var reg = new RegExp(/^[^@ ]+@[^@ ]+\.[^@ ]+$/);
  if(!fobj.elements['email'].value.match(reg))errors += 'Invalid Email Address!\n';

  if (errors.length > 0) {
    alert(errors);
    return false;
  } else return true;
   
}
</script>
<table width="65%"  border="0" cellspacing="0" cellpadding="0">

      <tr>
<form method="post" action="mail.php"  name="frmmail"  onsubmit="return isValid();">
        <td colspan="3"><h3 >Contact Form  </h3>
          <span class="contact1"><b>(All fields are Mandatory)&nbsp;&nbsp;&nbsp;</b></span><b>&nbsp;</b>
 
 <table width="73%"  border="0" cellpadding="3" cellspacing="4">

        <tr>

            <td width="15%" align="right" valign="middle" class="contact1"> Name&nbsp;&nbsp;&nbsp;&nbsp;</td>

            <td width="85%"><input name="name" type="text" style="width:200px " ></td>
          </tr>

          <tr>

            <td align="right" valign="middle" class="contact1"> E-mail&nbsp;&nbsp;&nbsp;&nbsp;</td>

            <td><input name="email" type="text" style="width:200px " ></td>
          </tr>

          <tr>

            <td align="right" valign="middle" class="contact1">Subject&nbsp;&nbsp;</td>

            <td><input name="subject" type="text" maxlength = "100" style="width:200px "></td>
          </tr>

          <tr>

            <td align="right" valign="middle" class="contact1">Message</td>

            <td><textarea name="message" rows="5" style="width:200px "></textarea></td>
          </tr>

          <tr>

            <td height="30" align="right">&nbsp;</td>

            <td><input type="submit" value="Submit" name="cmdsubmit"></td>
          </tr>
      </table>  </td>
      </form></tr>
 
    </table>