Question: what is the difference between the three domain system and the five kingdom system?
Answer: The five kingdoms still exist. It's just that they've been reclassified under three domains: Archae, Bacteria, and Eukaryota. Basically, the domains are classified by cell structure; the Eukaryotes have nucleuses and membrane-bound organelles, while Archae and Bacteria don't but vary from each other in some other way.