Not a valid MySQL result?

1

i dont know what this lines want to tell me:

Warning: mysql_num_rows(): supplied argument is not a valid MySQL result resource in C:\apachefriends\xampp\htdocs\personen.php on line 15
Datensätze gefunden

Warning: mysql_fetch_assoc(): supplied argument is not a valid MySQL result resource in C:\apachefriends\xampp\htdocs\personen.php on line 20
i simply made a db called “firma” with table “personen” looks like this(without the brackets):

name(lastname)
vorname(firstname)
personalnummer(number of staff)
gehalt(salery)
geburtstag(birthday)

here is the php:

<html>
<body>

<?php
mysql_connect();

mysql_select_db(“firma”);

$res=mysql_query(“select * from personen”);

[COLOR=Red] $num=mysql_num_rows[/COLOR](mysql_query(“select * from personen”));
echo “$num Datensätze gefunden<br>”;

while ([COLOR=Red]$dsatz=mysql_fetch_assoc/COLOR)
{
echo $dsatz[“name”] . ", "
. $dsatz[“vorname”] . ", "
. $dsatz[“personalnummer”] . ", "
. $dsatz[“gehalt”] . ", "
. $dsatz[“geburtstag”] . “<br>”;
}
?>

</body>
</html>

ive no idea what to do now