what's wrong here?:) I want to put data to database (I'm pretty sure that connection to db works).
$host="localhost";
$username="root";
$password="root";
$db_name="db";
$tbl_name="changes";
mysql_connect("$host","$username","$password")or die("cannot connect");
mysql_select_db("$db_name")or die("cannot select DB");
$when=$_POST['when'];
$bad_teacher=$_POST['bad_teacher'];
$teacher=$_POST['teacher'];
$hour=$_POST['hour'];
$class=$_POST['class'];
$sql="INSERT INTO $tbl_name (when, bad_teacher, teacher, hour, class) VALUES (`$when`,`$bad_teacher`,`$teacher`,`$hour`,`$class`)";
mysql_query($sql);
?>
WHEN is mysql reserved keyword you need to use bactiks arround your column names matched with Rererved Keywords,and why you have used bacticks arround the values.
$sql="INSERT INTO
$tbl_name (`when`, `bad_teacher`, `teacher`, `hour`, `class`)
VALUES
('".$when."','".$bad_teacher."','".$teacher."','".$hour."','".$class."')";
Also mysql* family is depreiciated you need to move on with pdo or aleast with mysqli* family.
Pdo demo
$dbhost = "localhost";
$dbname = "dbname";
$dbuser = "user";
$dbpass = "pass";
// database connection
$conn = new PDO("mysql:host=$dbhost;dbname=$dbname",$dbuser,$dbpass);
// query
$sql = "INSERT INTO books (`when`, `bad_teacher`, `teacher`, `hour`, `class`)
VALUES (:when,:bad_teacher,:teacher,:hour,:class)";
$q = $conn->prepare($sql);
$q-> bindParam(':when', $when);
$q-> bindParam(':bad_teacher',$bad_teacher);
$q-> bindParam(':teacher', $teacher);
$q-> bindParam(':hour', $hour);
$q-> bindParam(':class', $class);
$q->execute();