I like beer: Lubie piwo - But I don't like beer: Nie lubie piwa
in the Polish language nouns get declined - meaning they acquire new endings for different 'cases' and sometimes (less often) experience a change to the core of the word - which case is used in a sentence is typically governed by the verb or the position in the sentence - typically the active side (the subject of the sentence) is in the case known as 'nominative' - in Polish dictionaries words are listed by their nominatives - there are 6 other 'cases' - in this case the verb 'lubię' requires the accusative form/'case' - it happens so that the nominative and accusative of 'piwo' are the same - however the negation of verbs typically requires a different 'case', namely genitive - the genitive of 'piwo' is 'piwa' - in the singular 'piwo' may go under all these forms: piwo, piwa, piwu, piwie, piwem depending on the role in the sentence (whether it is a subject or object of the verb/sentence and depending on the verb in question - various verbs require different cases also various pronouns (in, above, under, around, on etc) require particular cases of the noun that they are attached to