As stated by @Molot this should not be used generally. Recommended methods would be db_insert and db_merge.
Placeholders are layed wrong, they need to be in single array. Use
$sql = "INSERT INTO {customers} (first_name,last_name,email_addr,password)
VALUES(:fName, :lName, :email , :cpwd)";
db_query($sql,
array(
':fName' => $form_state['values']['fName'],
':lName' => $form_state['values']['lName'],
':email' => $form_state['values']['email'],
':cpwd' => $form_state['values']['cpwd'],
),
);