Watashitachi - means we, us. Since in Japanese the word order is different than in English, to say 'we are' you use the following format: Watashitachi wa (what you are) desu. 'wa' is a subject marker. (It directly follows the subject) 'desu' is a copula. (It links the explanation to the subject) Desu is usually translated into English as 'is' or 'are'. There is no difference between 'is' and 'are' in Japanese as far as I can tell. For example: Watashitachi wa ureshii desu. - We are happy. Wareware wa kanashii desu. - We are sad. If you wanted to say 'I am', you would use the same format.