kaigi ga hazimaru mae ni, butyou ni siryou wo watasimasita.

Because with 前に, Japanese normally uses the dictionary form of the verb to mean before doing / before something happens.

So:

• 会議が始まる前に = before the meeting starts / started
• 会議が始まった前に would be incorrect here

The key idea is that 前に looks at the event as something that has not happened yet at that point. From the viewpoint of handing over the materials, the meeting had not started yet, so Japanese uses 始まる.

A useful pattern is:

• Verb (dictionary form) + 前に = before doing
• Verb (た-form) + 後で / あとで = after doing

For example:

• 食べる前に = before eating
• 食べた後で = after eating

前に means before.

In this sentence, it connects two actions:

• 会議が始まる = the meeting starts
• 部長に資料を渡しました = (I) handed the materials to the department head

So the first part tells you when the second action happened:

• 会議が始まる前に、部長に資料を渡しました。
• Before the meeting started, I handed the materials to the department head.

It is functioning as a time expression.

The に marks the time point that the main action relates to.

So:

• 会議が始まる前に = before the meeting starts
• the main action 渡しました happened at that time reference

You can think of 前に as a fixed grammar pattern meaning before.

A similar use appears in other time expressions:

• 3時に行きます = I’ll go at 3
• 出かける前に、電話します = I’ll call before going out

In casual speech, particles sometimes get dropped, but in standard grammar 前に is the normal form here.

Here, 会議が始まる is the natural way to describe the event “the meeting starts.”

が marks 会議 as the subject of 始まる.

• 会議が始まる = the meeting starts

Using は is possible in some contexts, but it changes the nuance. は would sound more like you are setting up the meeting as a topic or contrast:

• 会議は始まる前に... would sound unusual here without a special contrastive context

In this sentence, you are simply describing the event that serves as the time reference, so が is the most natural choice.

Because 始まる is directly modifying 前 as part of a clause.

Japanese often puts a plain-form verb directly before a noun:

• 食べる時間 = time to eat / time when someone eats
• 読む本 = a book to read / a book that someone reads
• 会議が始まる前 = the time before the meeting starts

So 始まる前 is a normal clause + noun structure.

By contrast, when you attach 前 to a noun, you use の:

• 会議の前に = before the meeting

So compare:

• 会議の前に = before the meeting
• 会議が始まる前に = before the meeting starts

The second version is more specific because it describes the event of the meeting beginning.

That に marks the recipient of the action 渡す.

• 部長に = to the department head
• 資料を = the materials
• 渡しました = handed over / gave

So:

• 部長に資料を渡しました
• (I) handed the materials to the department head

This is very common with verbs of giving, showing, sending, and telling:

• 先生に宿題を出しました = I submitted homework to the teacher
• 友だちにメールを送りました = I sent an email to my friend

Because 資料 is the direct object of 渡しました.

• 資料を渡しました = handed over the materials

With 渡す, the thing being handed over takes を, and the person receiving it often takes に:

• A に B を 渡す
• give/hand B to A

So in your sentence:

• 部長に = to the department head
• 資料を = the materials
• 渡しました = handed over

Yes, the natural interpretation is “I handed the materials to the department head before the meeting started.”

Japanese often omits the subject when it is clear from context.

So even though there is no explicit 私が or 私は, listeners naturally understand the subject from the situation.

This is extremely common in Japanese. A full version would be:

• 私は会議が始まる前に、部長に資料を渡しました。

But in most real conversation, 私は would be omitted unless needed for emphasis, contrast, or clarity.

渡しました is the polite past form of 渡す.

• dictionary form: 渡す
• polite non-past: 渡します
• polite past: 渡しました

It is in the past because the main action of the sentence is something that was completed:

• the materials were handed over

The sentence is also in the ます-form, which makes it polite. That is appropriate in many neutral or formal situations, especially in textbook Japanese.

So the sentence combines:

• a time clause: 会議が始まる前に
• a main past action: 部長に資料を渡しました

Yes, you could, but the nuance is slightly different.

• 会議の前に = before the meeting
• 会議が始まる前に = before the meeting starts

In many situations, they mean almost the same thing. But 会議が始まる前に is a little more explicit and event-focused: it refers specifically to the point before the meeting begins.

For example:

• 会議の前に資料を渡しました。
  I handed over the materials before the meeting.

• 会議が始まる前に資料を渡しました。
  I handed over the materials before the meeting started.

The second one highlights the start of the meeting more directly.

Not completely. Japanese word order is more flexible than English, as long as the particles make the roles clear.

The basic sentence is:

• 会議が始まる前に、部長に資料を渡しました。

You could also say:

• 部長に、会議が始まる前に、資料を渡しました。
• 資料を、会議が始まる前に、部長に渡しました。

These are all understandable because:

• が marks the subject of 始まる
• に marks the recipient
• を marks the direct object

That said, some orders sound more natural than others depending on emphasis. The original version is very natural and clear.

部長 usually means department head, division manager, or sometimes simply manager, depending on context.

Japanese often leaves out information like the, a, my, our, etc., if the meaning is clear from context.

So:

• 部長に could mean
  
  • to the department head
  • to my manager
  • to our department head

The exact English translation depends on the situation.

This is normal in Japanese. The language often leaves context-dependent details unstated, while English usually requires you to choose something.

Yes. 資料 is a broad word, and the best translation depends on context.

Possible translations include:

• materials
• documents
• handouts
• papers
• reference materials

In a business or meeting context, documents or materials are both very natural.

So this sentence could also be translated as:

• Before the meeting started, I handed the documents to the department head.

That may even sound more natural in some contexts than materials.