For how to insert into there's a nice article here
http://www.w3schools.com/php/php_mysql_insert.asp
INSERT INTO table_name (column1, column2, column3,...)
VALUES (value1, value2, value3,...)
//not sure if this will make a difference buy i would try a space between tax_id) and values(
also, im not sure if the way youve done it is wrong but i would have written like this
if(isset($id))
{
$qry = "insert into user_to_birds (user_id, tax_id)
values( '1' ,'".$id ."') ";
$result = mysql_query($qry);
}
look at string concatination aswell either have
" ' ' ".$variable." ' ' ";
in that fashion