"Desu" translates as "It is" Arimasu and imasu are translated to something existing. Arimasu is used for non-living things while imasu is used for things that are alive. for example you can say " pen wa arimasu ka" which is literally " do you have a pen? or "does a pen exist?" if you said "pen desu ka" then it just means "is it a pen?" imasu would be used, for example asking if you have a dog. " inu ga imasu ka?" Hope that makes sense ^^