Конференция проходит в том же зале, где вчера была лекция.

In this sentence, проходит means takes place, is being held, or is going on.

The verb is проходить, and although it often literally means to pass or to go through, it is very commonly used with events:

• Концерт проходит в парке. = The concert is taking place in the park.
• Встреча проходит утром. = The meeting takes place in the morning.

So Конференция проходит... is a very natural way to say The conference is taking place...

Russian often uses the present tense for an event that is happening now or is currently underway.

So:

• Конференция проходит... = The conference is taking place...

This does not necessarily mean a repeated action. It can simply describe what is happening at the present time.

If you wanted a past meaning, you would use a past form:

• Конференция проходила... = The conference was taking place / took place...

Because в can take different cases depending on meaning:

• в + accusative = motion into
• в + prepositional = location in

Here there is no movement. The conference is in the hall, so Russian uses the prepositional case:

• зал → в зале

And since том же describes зале, it must also be in the same case:

• тот → том
• же stays the same

So:

• в том же зале = in the same hall

Compare:

• Мы идём в тот же зал. = We are going into the same hall.
• Мы находимся в том же зале. = We are in the same hall.

том же is how Russian says the same here.

It is made of:

• том = a form of тот (that)
• же = a particle that adds the idea of same / very / exactly

Together, тот же literally means something like that same.

Because зал is masculine singular and here is in the prepositional case, тот же changes to match it:

• nominative: тот же зал
• prepositional: в том же зале

So:

• в том же зале = in the same hall

In this sentence, же is important because it gives the meaning same.

Compare:

• в том зале = in that hall
• в том же зале = in that same hall / in the same hall

So if you remove же, the meaning changes. You would no longer be saying the same hall, just that hall.

Где means where, and here it introduces a relative clause that describes зале.

So:

• в том же зале = in the same hall
• где вчера была лекция = where the lecture was yesterday

Together:

• в том же зале, где вчера была лекция = in the same hall where the lecture was yesterday

This is a very normal Russian structure.

Russian word order is flexible, and different orders can sound more natural depending on what is being emphasized.

In где вчера была лекция, the structure is very natural for introducing the event after setting the place/time frame:

• где = where
• вчера = yesterday
• была лекция = there was a lecture / the lecture was

This can sound a bit like where yesterday there was a lecture.

You could also say:

• где вчера лекция была

but that is less neutral and may sound more marked or conversational, depending on context.

So где вчера была лекция is the most standard and natural choice here.

Because лекция is a feminine noun, and in the past tense Russian verbs agree with gender in the singular.

So:

• masculine: был
• feminine: была
• neuter: было

Since лекция is feminine:

• вчера была лекция = yesterday there was a lecture

Both are possible, but they are slightly different in feel.

• была лекция = there was a lecture
• проходила лекция = a lecture was taking place / was being held

In this sentence, была лекция is simple and natural. It just identifies what happened in that hall yesterday.

If you said:

• Конференция проходит в том же зале, где вчера проходила лекция,

that would also be grammatical, but it sounds a bit more formal or repetitive because проходит / проходила appears in both clauses.

So была лекция is often the smoother choice.

Because где вчера была лекция is a subordinate clause describing зале.

Russian separates this kind of clause with a comma:

• Конференция проходит в том же зале, где вчера была лекция.

This is similar to English:

• The conference is taking place in the same hall, where there was a lecture yesterday.

Even though English punctuation may vary depending on style, in Russian the comma is required here.

Yes, but it means something slightly different in nuance.

• в том же зале = in the same hall
• в одном и том же зале = in one and the same hall

The longer version is more emphatic. It stresses that it is exactly the same place.

In your sentence, в том же зале is the most natural and standard phrasing.

Yes: English uses same as a single word, but Russian usually expresses this idea with тот же.

So learners often need to remember:

• same hall → тот же зал
• in the same hall → в том же зале

It is not usually translated word-for-word with one adjective. Instead, Russian uses the demonstrative тот plus the particle же.