In Russian "A — это B" is your typical construction for definitions ("Tortoises are a family of reptiles"). Or for emphasis, like "Солнце — это жизнь" (Sun is life).
Note that is such construction you cannot swap A and B, just like in English it would be weird to read a "definition" like "A family of reptiles with a shell are Tortoises". You don't have to translate this construction into English, as it is usually clear from the left and right part that the sentence is some kind of definition.
Many languages do without the articles, for instance, Japanese. Such details only lead to problems when a translation is what bothers you. In real life people tend to use just enough words to express the meaning, generally aware what the listener knows and what they don't. Or telling more if the listener is unaware. For translation, short sentences become extremely context-sensitive. An easy example would beOn a side note: a lot of other languages tend to make a distinction between "a" and "the" such as a car means any car but the car means is used when a particular car is the subject, how do you make this distinction in Russian or is that purely left down to этот
"У кого есть учебник?" vs. "У кого учебник?"
You see, in Russian it is typical to NOT use "есть" to express "having" some object that is known to exist. For example, "У тебя красивые ноги". People tend to have legs, so HAVING them is out of question, it is their properties that are. So, back to books, "У кого есть учебник?" is a rough equivalent of "Who's got a textbook?", and "У кого учебник?" is a rough equivalent of "Who has got the textbook?" (because in the latter case the sentence is formed as though it is already known that there is some textbook we are talking about). Such things are all over the laguage. But, indeed, many sentences are hard to translate when a handful of words is all you got. To make it more obvious: in Japanese Present and Future are exactly the same "non-past" tense. Without any words like "tomorrow", "next week", "after 2 years" you can only guess if you don't know the context in which the sentence arised.
That actually means "You can buys apple trees in stores". The correct sentence is "Ты можешь купить яблоки в магазине". But a more natural variant is to use "можно": "Яблоки можно купить в магазине".