What do they mean and how do you use them? This article by The Straits Times gives a few example sentences. But being rather isolated sentences, it doesn't quite give the full idea. I decided to do a short dialogue example instead:
*Ah Boy goes into a shop with a friend*
*takes out shopping list*
Ah Boy: "Uncle, dis one, have anot?"
Owner: *thinks a while* "Dun have leh."
Ah Boy: "Har!? Dun have meh?"
Owner: *searches around* "Dun have lah!"
Ah Boy: "Dis one leh?"
Owner: "Dun have liao."
Ah Boy: "So fast ah?"
Owner: "Popular mah."
Ah Boy: "Liddat, den dis one dun have hor?"
Owner: "Gone loh."
Ah Boy: *turns to friend* "Dun have siah!"
Friend: "Told you dun have one lor!"