Я записываю всё, что говорит учитель.

Записываю means I write down / I note down. It comes from записывать, which often means writing something down so you do not forget it.

That is different from пишу, which is the more general I write.

So:

• Я пишу письмо. = I am writing a letter.
• Я записываю адрес. = I am writing down the address.

In your sentence, записываю is used because the idea is noting down what the teacher says.

Записываю is the 1st person singular present-tense form of the imperfective verb записывать.

It matches Я = I, so the ending shows I am doing the action:

• я записываю = I write down / I am writing down
• ты записываешь = you write down
• он/она записывает = he/she writes down

Because it is imperfective, it can describe:

• an action happening now: I am writing down
• a repeated or habitual action: I write down

Because всё means everything, while все usually means everyone or all in the plural.

Compare:

• всё = everything
• все = everyone / all people / all things in plural depending on context

So here:

• Я записываю всё... = I write down everything...

That is exactly the form you need.

Also, ё is important here: всё is pronounced with stress on ё.

Here что means something like that or what in the expression everything that...

So:

• всё, что говорит учитель = everything that the teacher says

It is introducing a subordinate clause.

In other words, the structure is:

• всё = everything
• что говорит учитель = that the teacher says

So although что can mean what? in a question, here it is not a question word. It is functioning like a relative connector.

Because что говорит учитель is a subordinate clause, and Russian normally separates subordinate clauses with commas.

So the sentence is divided like this:

• Я записываю всё,
• что говорит учитель.

This is very normal in Russian. English sometimes uses fewer commas in similar sentences, but in Russian this comma is required.

Because the subject of that clause is учитель, and учитель is 3rd person singular.

So:

• учитель говорит = the teacher says / is saying

The verb говорить changes like this:

• я говорю = I say / I am saying
• ты говоришь = you say
• он/она говорит = he/she says

Since учитель is he/she grammatically in the sentence, you need говорит.

Because Russian has no articles. There is no direct equivalent of a or the.

So учитель can mean:

• a teacher
• the teacher

The exact meaning depends on context.

In this sentence, English naturally translates it as the teacher, but Russian does not need a separate word for that.

Grammatically, учитель is a masculine noun, and very often it refers to a male teacher.

For a female teacher, Russian often uses учительница.

However, in some contexts, masculine job titles can be used more generally, especially in older or more formal usage. Still, for everyday speech, if you clearly mean a woman, учительница is very common.

So in this sentence, without extra context, many learners would understand учитель as a male teacher or simply the teacher if gender is not the main point.

Yes. Russian often drops subject pronouns when the verb ending already makes the subject clear.

So both of these are possible:

• Я записываю всё, что говорит учитель.
• Записываю всё, что говорит учитель.

The version with Я is a little more explicit and can give slight emphasis to I.

English usually needs I, but Russian often does not.

It can be either, depending on context.

Because записываю is imperfective present, it can mean:

• I am writing down everything the teacher is saying — happening now
• I write down everything the teacher says — a usual habit

Russian often lets context decide between these two meanings.

Yes. Russian word order is fairly flexible, though the version you have is the most neutral and natural.

Your sentence:

• Я записываю всё, что говорит учитель.

Another possible version:

• Всё, что говорит учитель, я записываю.

This second version puts extra emphasis on everything that the teacher says.

So the basic meaning stays the same, but the focus changes.

The stress is:

• Я записы́ваю всё, что говори́т учи́тель.

A few useful pronunciation notes:

• ё in всё is always stressed.
• что is usually pronounced more like што, not a clear что.
• учитель has stress on the second syllable: учи́тель.

So a rough pronunciation guide would be:

• ya za-pee-SY-va-yu vsyo, shto ga-va-REET u-CHEE-tyel

This is only approximate, but it helps with the main stress and sound changes.