Yes, there are 6 cases in the Russian language. It means that we change endings of nouns, adjectives and pronouns according to the used verb or construction, to show what relationship there is between the words in a sentence. We need the cases that much because there is no strict word order in Russian sentences. English "I love you" can sound like "Я тебя люблю", "Тебя я люблю", "Я люблю тебя", "Люблю я тебя", "Люблю тебя я" in the Russian language. All the variants are correct and to be able to understand who loves whom we need to change the object into Accusative case. That's why we don't say "
Я люблю ты". One might change the word order and then it won't be understandable who does the action and who is the object of the action.
The names of the Russian cases are: Nominative (Именительный падеж), Genitive (Родительный падеж), Dative (Дательный падеж), Accusative (Винительный падеж), Instrumental (Творительный падеж) and Prepositional (Предложный падеж).
Nominative case is used to nominate, to name a thing or a person. A subject in a sentence is always in Nominative. Phrases like "Это…", "Вот…", "Где…?" have nouns in Nominative case. Let's say, it's an original form of a noun, the one you find in a dictionary if you want to look up a word.
Genitive case is used to say that somebody has, possesses something. To say that, we always start a sentence with "У" + Genitive: "У Сары есть мобильный телефон"(Sarah has a mobile phone). Genitive is also used to talk about what you don't have: "У меня нет + Genitive". There are lots of prepositions after which you must use Genitive as well: около, у, от, до and etc.
The main function of the Dative case is to show a recipient of an action. Like in English when you say "To whom?" (to call to whom, to text to whom, etc.). "Я звоню Марине" (I'm calling to Marina).
Accusative shows an object as in the "I love you" phrase "тебя" is in Accusative. Another important function is showing directions (to go TO WHERE?): "Я еду в Москву" (I go to Moscow) and not "
Я еду в Москва" or " Я еду в Москве".
Instrumental doesn't have one distinct function. From its name you can understand that among the other things it also shows an instrument: "Я пишу РУЧКОЙ" (I write using a pen), "Я ем суп ЛОЖКОЙ" (I eat soup with a spoon).
Prepositional mostly shows location, place, answers the question "Where". So if you want to say where you are, where you live, where you work and etc. use Prepositional case: "Я живу в Петрозаводске" (I live in Petrozavodsk).
To cheer you up a bit, there are more than 6 cases in most of the European languages, there are 15 in Estonian and even more in Hungarian. So… Russian is not that difficult as it seems! As soon as you get familiar with the endings of the cases and their usage Russian will be just like a piece of cake for you;)