IF ANYONE HAD GONE TO WAPANESE FOR WEEABOOS, "DESU" IS A VERB THAT SIMPLY MEANS "TO BE/IS."
I don't know how to categorize "desu". I guess it does mean something along the lines of "to be/is", but I wouldn't say that it refers to the item or person you're talking about. I would think "iru" or "aru" would be better for that description myself. I'm really not sure.
Example:
-
Pocky ga arimasuka?Do you have Pocky? (literally: Does pocky exist [here]?)
-
Hai, arimasuyoYes, we have some (literally: It exists [here])
-
Mack-san ga imasuka? Is Mack-san [existing] here?
-
Iie, imasenNo, he is not [existing here]
-
Kore wa nandesu ka?What is this?
-
Sore wa haniwa desu.That is a haniwa.
-
Sou desu ka?Really?
-
Sou desu yo.Yeah, really.
If you were asking the above question to a friend, it'd go more like this:
-
Kore wa nani?-What's that?
-
Haniwa da.A Haniwa.
-
Sou ka?Really?
-
UnnMm-hmm.
There's a reason why Japanese has the old nickname of "The Devil's Language" or something of the sort.