For Javascript validation please refer this link:  http://findnerd.com/account/#url=/list/view/Simple-Javascript-form-validation/15856/
 

FOR REGISTERING: Here is the code for registering the user and saving data in data.

<?php
     ob_start(); 
  		include "db.php";
  		extract($_POST);
  		if($_SERVER["REQUEST_METHOD"] == "POST")
  		{
          $sql = "SELECT * FROM emp where email = $email";
          $result = $conn->query($sql);
          if ($result->num_rows > 0) {
              echo "<script type='text/javascript'> alert('Username already registered')</script>";
          }
          else{
            $sql = "INSERT INTO emp (name,email,password) VALUES ('$name','$email','$password')";//use md5() for password to encrypt it
            if ($conn->query($sql) == TRUE) {
              header('Location:form.php');
              // echo "<script>location.href='form.php'</script>";
            }
            else{
              echo "<script type='text/javascript'> alert('Error: ". $sql."::". $conn->error."')</script>";   
            }  
          }
  		}
      $conn->close();
  	?>

In the above the file that I have included contains the connection to the database. First we have to check whether the username already exists in the database or not. For that I am getting data from the database by SQL SELECT query where the query matches the given username.

If the query does not return any value them i am inserting data into database.

FOR LOGGING IN: Here is the code for logging in-

	<?php
                ob_start();   
  		include "db.php";
  		extract($_POST);
  		if($_SERVER["REQUEST_METHOD"] == "POST")
  		{
			$sql = "SELECT * FROM emp where email = '$email' and password = '$password'";
			$result = $conn->query($sql);
			if ($result->num_rows > 0) {
				 // echo "<script>location.href='home.php'</script>";
				 header('Location:home.php');
			}
			else{
				echo "<script type='text/javascript'> alert('Incorrect s /PASSWORD')</script>";
			}
  		}
		$conn->close();
  	?>

Here i simply running a SQL query to select data from the database if the query matches the username and password.