I am not usually the type to say this, but you need to RTFM. It is very clear on http://www.php.net/. Check out the Time and Date functions that are built in.
You should also consider changing some varaiables. You have your database name as "date" and you have a field in your database with the name of "date", and you are inserting into "date", which seems to be your table name also? That's not quality programming.
Here is what I would do.
<?PHP
$time = time();
mysql_connect("","","")or die(mysql_error());
mysql_select_db("date_database")or die(mysql_error());
mysql_query("insert into date_table values('$id','$time')")or die(mysql_error());
$query = mysql_query("select * from date_table");
while($result=mysql_fetch_array($query))
{
echo($result["id"])." ";
echo date('d/m/y',$result["date_field"])."<br>";
}
?>