$password="123456";

md5($password);

Use md5(); to encrypts password to make it more secure

when you encryte "john856" using this code, you'll see this result
"ad65d5054042fda44ba3fdc97cee80c6" This is not a random result, everytime you encrypt the same password you will get the same result.

$password="john856";
$encrypt_password=md5($password);

echo $encrypt_password;

This is an example Login with encrypted password but don't forget to encrypt password and insert into database in sign up process.

// username and password sent from form
$myusername=$_POST['myusername'];
$mypassword=$_POST['mypassword'];

// encrypt password
$encrypted_mypassword=md5($mypassword);

$sql="SELECT * FROM $tbl_name WHERE username='$myusername' and password='$encrypted_mypassword'";
$result=mysql_query($sql);

You can learn to create login system here