It depends on names, Mary is a foreign name so we don't change it to fit the sentence: This is Mary - Ovo je Mary This is for Mary - Ovo je za Mary, Give this to Mary- Daj/ponesi ovo Mary; I think the appropriate name in Serbian language is Marija so for Marija we say: Ovo je Marija, Ovo je za Mariju, Daj ovo Mariji, Ovo je Marijino... You need to learn about declension