http://www.dentaldecks.com/Pages/Default.aspx
this is the website from where you can buy dental decks, or simply buy them second hand from someone who has already given the exam.
a flash card is a card which has a MCQ on one side and the answer with explanation and additional information on the reverse of the card. so you use these to prepare for the exam.
the information on the back of the exam is highly useful to clear NBDE (USA) or NDEB(Canada).
As for dental tutors they can probably help you when you get stuck on some tricky questions in the released question bank on NDEB website, apart from that you really have to study and go through all the reading material yourself.
also, dental decks come in part 1 (basic sciences) and part 2 (clinical sciences).