php - insert password into database in md5 format?

can anyone please show me or explain how i can insert a password into a database in md5 format? even if you can just point me in the right direction or something i'd be grateful because I'm only new to mysql thanks.

$query="INSERT INTO ptb_users (id,
user_id,
first_name,
last_name,
email )
VALUES('NULL',
'NULL',
'".$firstname."',
'".$lastname."',

'".$email."',
'".$password."'
)";
mysql_query($query) or dieerr();
$result = mysql_query("UPDATE ptb_users SET ptb_users.user_id=ptb_users.id");

Answer

use MD5,

$query="INSERT INTO ptb_users (id,

user_id,
first_name,
last_name,
email )
VALUES('NULL',
'NULL',
'".$firstname."',
'".$lastname."',
'".$email."',
MD5('".$password."')

)";

but MD5 is insecure. Use SHA2.