"desu" can be used to end the sentence with a slight polite way. like watashi-no ie-desu わたしの　いえです。 watashi-no haha-desu　わたしの　ははです。 watasi-ga suki-na manga-desu　わたしの　すきな　まんがです。 koneko-wa kawaii-desu　こねこは　かわいいです。 nihon-ga suki-desu　にほんが　すきです。 "imasu" can be divided 2part like this [i-masu] [i(iru)] -is a kind of copula. the function is similar with linking verb (is,am, are) "masu" can make the verb polite. iki-masu 行きます、いきます(I'm going to go.) yomi-masu 読みます、よみます(I'm reading.) mi-masu 見ます、みます(I'm seeing.) tabe-masu食べます、たべます(I'm eating.) This "masu”-form always come at the end of a complete sentence. desu-form and masu-form can make a polite sentence in Japanese. watashi-wa iku →watasi-wa iki-masu watashi-wa taberu→ watashi-wa tabe-masu watashi-wa yomu →watashi-wa yomi-masu

desu is used to express the "copula",the verb to be in english. example: "Christy-san wa ii desu."(Christy is fine,is good,okay.) "Christy-san wa ii desu ka?"(this ka means a question,so all the things turn into a question like : Is Christy fine?) "imasen"(negative) "imasu"(affirmative) imasu is a verb which means to exist(only for living things like,a cat,dog,persons and etc) "koko wa neko ga imasu ka?" (Is an cat there?) I`m a japanese learner like you,but i think this is the right answer,if someone(native speaker) see this,and say that is wrong,please point why!! thanks!

imasu = somebody is somewhere desu = hundreds of meanings, but generally serves as the copula in the phrase: "this is that".

I think “desu”means“is”,“imasu”means“someone is here”.For example,“あの人は男desu”means“That person is a man”,“ここにいますか？”means“Is he here？”.In fact,there are some different usage between two words.But I don't know all useage because I haven't learned Japanese.Sorry,I can't help you.