Learn Hardcore Russian: Ты когда‑нибудь была на концерте в Большом театре? - Have you ever been to a concert at the Bolshoi Theatre?

Russian doesn’t have a separate present perfect tense like English (have been, have seen, etc.).
For “have you ever been”, Russian simply uses the past tense of быть (был / была / были) plus an adverb like когда‑нибудь or уже.
So Ты когда‑нибудь была…? literally is “Were you ever…?”, but in context it covers the English “Have you ever been…?” meaning.

Why is it была and not был? What would change if I talk to a man or to several people?

Была is the feminine past form of быть; it’s used when you’re talking to a female.
If you’re talking to a male, you say: Ты когда‑нибудь был на концерте в Большом театре?
If you’re talking to more than one person (or formal вы), you use the plural:
Вы когда‑нибудь были на концерте в Большом театре?

What exactly does когда‑нибудь mean here? Is it the same as “ever” in English?

In questions like this, когда‑нибудь is very close to English “ever”: “at any time (in your life)”.
Literally it’s “at some time or other, at some unspecified time.”
It’s common in questions and conditionals: Ты когда‑нибудь был…?, Если ты когда‑нибудь приедешь…
So here: Ты когда‑нибудь была…? ≈ “Have you ever been…?”

What’s the difference between когда‑нибудь and когда‑то? Could I say Ты когда‑то была…?

You could say Ты когда‑то была на концерте в Большом театре?, and it would be understood.
Nuance:

Когда‑нибудь in a question usually focuses on “ever, at any point in your life”.
Когда‑то more often feels like “once, at some time in the past” and often implies that it did happen, you’re just not saying when.

So когда‑нибудь is the more neutral, typical choice for an “Have you ever…?” question.

Can I change the word order, e.g. Ты была когда‑нибудь на концерте…? Does that sound natural?

Yes, you can say Ты была когда‑нибудь на концерте в Большом театре? and it’s still natural.
The most neutral order is probably the original: Ты когда‑нибудь была… (putting когда‑нибудь right after ты).
Moving когда‑нибудь later slightly shifts the rhythm/intonation but doesn’t really change the meaning.
Russian allows quite flexible word order; intonation carries a lot of the emphasis.

Why is it на концерте and not в концерте or на концерт?

Russian uses на with many events and activities: на концерте, на выставке, на лекции, на вечеринке = “at a concert / exhibition / lecture / party.”
Here we’re talking about being at an event in a static sense, so we use на + prepositional case: на концерте.
На концерт (accusative) would mean “to a concert” (movement, going to).
В концерте is rare and would mean “in the concert” in the sense of taking part in it (e.g. участвовать в концерте).

Why does концерте end in ‑е?

Концерт is a masculine noun.
After the preposition на (with the “location” meaning on/at), masculine and neuter nouns usually take the prepositional case, which for most such nouns ends in ‑е.
So: на концерте, на уроке, на пляже, на заводе.
Here на концерте = “at the concert.”

Why do we say на концерте but в Большом театре — two different prepositions for “at”?

Russian often uses на for events/activities and в for physical spaces/inside places.

на концерте – at a concert (event)
в театре – in/at the theatre (building/place)

So на концерте в Большом театре literally combines both ideas: “at a concert (event) in the Bolshoi Theatre (place).”

Why is only Большом capitalized in в Большом театре, not театре?

In Russian, in many names of institutions the first word of the name is capitalized, and the following generic noun (театр, музей, университет) is often lower‑case.
Большой театр is literally “The Big Theatre,” where Большой is the distinctive part of the name and театр is a common noun.
So you often see: в Большом театре (capital Б, lower‑case т), just like in your sentence.
Stylistic rules can vary a bit, but this spelling is common and correct.

Could I just say Ты была на концерте в Большом театре? without когда‑нибудь? Does it still mean “Have you ever been…”?

Without когда‑нибудь, the sentence is more like “Were you at a concert at the Bolshoi Theatre?”
It usually refers to some specific time (maybe one you both know about from context) rather than your entire life experience.
Adding когда‑нибудь explicitly widens the time frame to “at any point in your life, ever.”

Why don’t we need any extra word like ли or word order change to make this a yes/no question?

Russian yes/no questions usually have the same word order as a statement and are marked mainly by intonation.
Statement: Ты когда‑нибудь была на концерте в Большом театре.
Question: Ты когда‑нибудь была на концерте в Большом театре? (rising intonation).
The particle ли is possible but less common and more formal/marked here: Была ли ты когда‑нибудь…? – that sounds bookish or stylistic, not neutral conversational Russian.

Could I say на концерте Большого театра instead of на концерте в Большом театре? Is there a difference?

Yes, but the meaning changes slightly.

на концерте в Большом театре – at a concert that is taking place in the Bolshoi Theatre (location).
на концерте Большого театра – at a concert given by / organized by the Bolshoi Theatre (the concert belongs to that theatre; it might even be in another city).

In your sentence, the focus is on the place, so в Большом театре is the natural choice.

Where is the stress in the words когда‑нибудь, была, and театре?

когда‑нибудь → когда́‑нибудь (main stress on да; нибудь is usually unstressed here).
была → была́ (stress on the last syllable).
театре → теа́тре (stress on а: те‑ат‑ре).

Pronounced together naturally: Ты когдá‑нибудь былá на концéрте в Большóм теáтре?