The Genitive case is used after certain prepositions:
Попросќте у Мђши стакђн. Ask Masha for a glass.
У Мђши љсть стакђн? Does Masha have a glass?
Вћт письмћ от Мђши. Here's a letter from Masha.
Вћт письмћ из МосквІ. Here's a letter from Moscow.
салђт из фрџктов a fruit salad (i.e. 'a salad made from fruit')