Hello, dear student! Talking about cases in the Russian language, my students often ask me about the prepositional case. Some "advanced" students already understand and distinguish the questions of every case in Russian. However, there are common situations in speech, when it is difficult for a foreigner to define a case because we, Russian-speaking people, make it by intuition and do not think of what question we should ask or sometimes even should not. Let's look at the example:
Большая машина стояла за деревом [Bal'shaya mashina stayala za derevam] - There was a big car behind the tree.
Let's define the cases of our nouns,
Что? Большая машина (What? a big car) - in the nominative case because it answers the corresponding question
За деревом (behind the tree) - here we want to ask by intuition the question "где?" (where?). In fact, it is correct, but if we want to define case, it would be more correct to ask "за чем?" (behind what?). Pay attention, we write "за чем" (где) in two words. Do not mix up this question with another one which sounds similar - "зачем" (for what purpose?)
To not let this confusion happen, you should learn some situations with prepositions, when noun is in the prepositional case:
1. After the preposition "перед" [perid]:
Перед домом [Pered domam] - In front of the house
2. After the preposition "за" [za]:
За стеной у нас еще одна комната [Za stinoj u nas ishyo adna kamnata] - There is another room behind the wall in our house.
3. After the preposition "над" [nad]:
Над пропастью [Nad propastyu] - Above the precipice
4. After the preposition "под" [pod]:
Коврик лежит под столом [Kovrik lizhit pad stalom] - The carpet is under the table
5. After the preposition "между" [mezhdu]:
Между нами тает лёд [Mezhdu nami tait lyot] - The ice is melting between us
Thus, learning these prepositions, you can always define the prepositional case. Of course, there are a lot of examples, when we use these prepositions in speech and if you are not sure what preposition to use in this or that situation, I recommend you to read the topic "Prepositions in Russian", too.