Unable to save data from custom drupal form
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' =&gt; $form_state['values']['fName'],
      ':lName' =&gt; $form_state['values']['lName'],
      ':email' =&gt; $form_state['values']['email'],
      ':cpwd' =&gt; $form_state['values']['cpwd'],
   )
);