Difference between arimasu and desu

Hello,
I started learning Japanese all by myself, and now something is not clear. I can't see the difference between arimasu and desu, because arimase= are, is, and desu= are, is, am. E.g. are these two sentences mean the same:
Doko ni shokudou ga arimasu ka?
and
Shokudou wa doko desu ka?
Are both of the correct? Please help me!
Thanks.

"arimasu = there are/is (thing/things), there exists...
"(place) ni arimasu" = there are ..... in (place), ... is/are located in (place)

As in:
- Watashi no gakkou ni wa ookii toshokan ga arimasu.
toshokan = library
(There is a large library at my school.)
- Tsukue no ue ni wa hon ga 3-satsu arimasu. (There are three books on the desk.)

Either of:
- Shokudou wa doko ni arimasu ka?
- Shokudou wa doko desu ka?
.. can be used to ask "Where is the restaurant/cafeteria?"

Literally, the first one says "Where does the cafeteria exist?" and the second one "Where is the cafeteria?"

Please note that there may not be one-to-one correspondence between words in different languages, particularly between Western languages (including English) and Japanese, with vastly different grammar :) So it would help if you don't learn "arimasu = are, is" and "desu = are, is, am," etc. but in sentence context. Enjoy learning!