zyugyoutyuu ni wakaranaikoto ga attara, sensei ni situmon wo simasu.

授業中 means during class / in the middle of class.
The particle に marks the time or situation in which something happens.

So:

• 授業中に = during class
• 授業中に質問をします = I ask a question during class

In everyday Japanese, you may also hear 授業中, without に, in some contexts, but 授業中に is very standard and clear here.

授業中 is made from:

• 授業 = class, lesson
• 中 = middle, ընթացքում / during

Together, 授業中 means in class or during class.

It is a common pattern:

• 会議中 = during a meeting
• 仕事中 = while working / at work
• 食事中 = during a meal

So 授業中に is a very natural way to say during class.

こと turns the idea before it into a thing / matter / something.

• 分からない = not understand / unclear
• 分からないこと = something I don’t understand / something unclear

So instead of just saying I don’t understand, this phrase creates a noun-like expression:

• 分からないことがある = there is something I don’t understand

This is very common in Japanese. Other examples:

• 心配なこと = something I’m worried about
• やりたいこと = something I want to do
• 必要なこと = something necessary

This is a very common learner question.

• 分からない = I don’t understand / I don’t know the answer / it’s unclear to me
• 知らない = I don’t know it because I have not learned/heard it

In a classroom, if you are confused about the lesson, 分からない is usually the better choice.

For example:

• この文法が分かりません。 = I don’t understand this grammar.
• その言葉を知りません。 = I don’t know that word.

So here, 分からないこと means something I don’t understand, which fits the classroom situation very well.

In 分からないことがあったら, the が marks the thing that exists.

The basic pattern is:

• Noun が ある = there is / there exists a noun

So:

• 分からないことがある = there is something I don’t understand

You would not normally use を with ある in this structure, because ある is not taking it as a direct object here. It is expressing existence.

あったら comes from ある and means if there is or if there happens to be.

Breakdown:

• ある = to exist, to have
• あった = past form
• あったら = conditional form based on the past form

Even though it uses a past-looking form, あったら often means if there is / if there are in English.

So:

• 分からないことがあったら = if there is something you don’t understand

This pattern is extremely common:

• 時間があったら、行きます。 = If I have time, I’ll go.
• 質問があったら、聞いてください。 = If you have a question, please ask.

This is just how one common Japanese conditional is formed.

The -たら conditional is made from the past short form + ら:

• 行く → 行ったら = if/when [someone] goes
• 食べる → 食べたら = if/when [someone] eats
• ある → あったら = if there is / if there was

So it is called the tara conditional.
It does not necessarily mean the whole sentence is in the past.

In this sentence, あったら expresses a condition:

• If there is something I don’t understand, ...

Yes, 分からないことがあれば is also grammatical and natural.

The difference is mostly nuance:

• あったら sounds a bit more conversational and concrete: if there is / if something comes up
• あれば can sound a little more formal, neutral, or general

So both are fine:

• 分からないことがあったら、先生に質問をします。
• 分からないことがあれば、先生に質問をします。

In beginner materials, 〜たら often appears early because it is very common in everyday speech.

Here, に marks the target / person toward whom the action is directed.

• 先生に質問をします = ask the teacher a question

So に is like to in English:

• 友だちに聞きます = ask a friend
• 先生に相談します = consult the teacher
• 母に電話します = call my mother

In this sentence, the teacher is the person receiving the question.

Japanese often uses a noun + する pattern where English uses a simple verb.

• 質問 = question
• 質問をする = to ask a question

So 先生に質問をします literally looks like:

• do a question to the teacher

But in natural English, it means:

• ask the teacher a question
• or simply ask the teacher

This pattern is very common:

• 勉強をする = study
• 運動をする = exercise
• 説明をする = explain / give an explanation

Yes, often you can, but the nuance is a little different.

• 質問をします focuses on asking a question
• 聞きます means ask or listen/hear, depending on context

In a classroom:

• 先生に質問をします = I ask the teacher a question
• 先生に聞きます = I ask the teacher

Both can work, but 質問をします is slightly more explicit and formal-sounding, because it clearly says ask a question.

Japanese non-past forms like します can mean:

• present/habitual: I do / I usually do
• future: I will do

In this sentence, it often sounds habitual or general:

• If there is something I don’t understand during class, I ask the teacher.

But depending on context, it could also describe a future intention:

• If there is something I don’t understand during class, I’ll ask the teacher.

Japanese often leaves that distinction to context.

Japanese very often puts the condition before the main result.

So the structure is:

• [condition] + [main action]

Here:

• 分からないことがあったら = if there is something I don’t understand
• 先生に質問をします = I ask the teacher a question

This is one of the most common sentence patterns in Japanese.
English can also do this:

• If I don’t understand something, I ask the teacher.

So the word order is very natural for Japanese.

Yes, the subject is omitted, which is very normal in Japanese.

From context, the hidden subject is probably I:

• (私は) 授業中に分からないことがあったら、先生に質問をします。

Japanese often leaves out subjects when they are obvious.
So learners should get used to sentences where I, you, or they are not directly stated.

Here, the meaning is naturally understood as something like:

• If I don’t understand something during class, I ask the teacher.