I know all the good explanation about simple "IMASU" has already done above. However, for this sentence particularly, you have to know the function of "[verb]+TE+IMASU." If IMASU comes with verb+TE, it means 1. action in effect (the remaining state after something is done) 2. action in progress (present progressive) Kanojo wa toshi wo totte imasu. =She has already aged. (meaning (1) ) In Korean, "IMASU" is similar to "isseumnida." "-TE IMASU" is similar to "-a/eo isseumnida" or "-go isseumnida." "DESU" is similar to "imnida."

I was just rounding up my own notes about this today. I'm still pretty new to the language myself, but why not share them with you anyway, no? :) Neko desu -> It's a/the cat. Neko ga imasu -> There is a/the cat. Asoko ni neko ga imasu -> There goes a cat. It gets a bit trickier when dealing with 'doko' and such. For instance, you can say either these: Neko wa doko desu ka? -> Where is a/the cat? (in general) Neko wa doko ni imasu ka? -> Where is the cat? (its specific location) So, for asking about its specific whereabouts, I could ask: Neko wa teeburu no ue ni imasu ka? -> Is the cat on the table? (its specific location) We say, Mark desu -> I am Mark. Hence, Mark wa doko desu ka? -> Where is Mark? To simply ask where I 'am' (desu), as opposed to wanting to know at which specific location I am manifesting my physical existence (iru). But I since 'doko' denotes location anyway, asking where someone 'desu', in combination with 'doko', is inevitably, indirectly, also asking at which location that person 'is' (iru). So, if you wanted to really inquire about my physical whereabouts, you could say: Mark wa doko ni iru no? (Or "Doko ni iru ‘n desu ka?" and variants) -- Arimasu (aru) indeed is used for inanimate things, like: Hanashi ga arimasu -> We need to talk. (lit. "Talk (n) needs to exist.") However, as the ever helpful chihiro-san already pointed out, in a Present Progressive, you'd use IRU, regardless: Denwa de hanashite imasu. -> I’m talking on the phone. That's simply because the Present Progressive almost always uses 'te' + ‘iru’. Sometimes, you get 'te' + 'aru'. In one of my fav Amine, Macross Frontier, Ranka Lee sings a song with a line that goes like: Neko no nikki ni wa, o-hirune no kaisuu ga kaite aru. In the cat's diary, the number of its naps is written.

imasu was composed of "I" of "IRU" and "MASU" . IRU = exist MASU = be-verb at present. It is used to express equality and assertion to the subject and used at the end of the sentence. and The word "masu" is used in formal occasion or writing something and you shouldn't use it in informal occasion. MASITA= be-verb in the past derived from MASU. That's about the size of it . and You need to compare masu with desu if you compare .... I think it's too elementary ... you should read grammatical book. because its explanation could be sophisticated and checked by professional teachers many times before publication . and No doubt , it will help you more .

i am learning japanese but hope this helps. although they are similar they arent really interchangable, atleast not in expansive sentences. here is a youtube link on the subject http://www.youtube.com/watch?v=DebWy8NfEzw desu means "it is" or "is" or "are" imasu means the presence of a living thing.(i.e. cat dog person) more like "here is" or "there is" and arimasu is just like imasu except for non living things (i.e. walls floors mountains)