Мне нужно заточить карандаш перед уроком.

Because нужно is used in an impersonal pattern:

• мне нужно = it is necessary for me / I need to
• Literally, мне is in the dative case, not the nominative.

So Russian often expresses I need to do X as:

• Мне нужно + infinitive

Examples:

• Мне нужно уйти. = I need to leave.
• Мне нужно позвонить. = I need to call.

Using я here would not fit this structure.

Нужно means necessary, needed, or one needs to, depending on context.

In this sentence:

• Мне нужно заточить карандаш = I need to sharpen a pencil

It is a very common way to talk about necessity in Russian.

A useful pattern:

• мне нужно = I need to
• тебе нужно = you need to
• ему / ей нужно = he/she needs to
• нам нужно = we need to

So нужно itself does not change, but the pronoun changes.

This is about aspect.

• точить = imperfective
• заточить = perfective

Here, the speaker means to sharpen the pencil completely / as a finished action before the lesson, so Russian uses the perfective verb заточить.

Compare:

• Мне нужно заточить карандаш.
  I need to sharpen the pencil.
  → focus on completing the action

• Я точу карандаш.
  I am sharpening the pencil.
  → focus on the process

So заточить is natural because this is a one-time task with a result.

In this verb, за- helps form the perfective version of точить.

So:

• точить = to sharpen, to grind, to hone, as a process
• заточить = to sharpen completely / to get it sharpened

You do not always translate the prefix separately in English. Often the difference is just:

• imperfective = process / repeated action
• perfective = completed single action

So in this sentence, заточить suggests finish sharpening it.

Because it is the direct object of the verb, so it is in the accusative case.

But for an inanimate masculine noun, the accusative singular is usually the same as the nominative singular:

• nominative: карандаш
• accusative: карандаш

So the form does not change, even though the case does.

Compare with an animate masculine noun:

• Я вижу брата. = I see my brother.
  Here accusative changes to брата because the noun is animate.

But:

• Я вижу карандаш. = I see a pencil.
  No visible change, because карандаш is inanimate.

Because the preposition перед requires the instrumental case.

So:

• урок = lesson
• перед уроком = before the lesson

This is a fixed grammar rule:

• перед + instrumental

More examples:

• перед школой = before school / in front of the school
• перед обедом = before lunch
• перед экзаменом = before the exam

So уроком is the instrumental singular form of урок.

Here it means before the lesson in time.

The preposition перед can mean:

• before in time
• in front of in space

Context tells you which one is meant.

In this sentence:

• Мне нужно заточить карандаш перед уроком
• This clearly means I need to sharpen the pencil before class / before the lesson

It is about time, not physical position.

Yes, Russian word order is more flexible than English.

The neutral order here is:

• Мне нужно заточить карандаш перед уроком.

But other orders are also possible, depending on emphasis:

• Перед уроком мне нужно заточить карандаш.
  Emphasis on before the lesson

• Карандаш мне нужно заточить перед уроком.
  Emphasis on the pencil

Even though word order can move around, the original version sounds natural and neutral.

Yes. Надо and нужно are often very similar.

• Мне нужно заточить карандаш = I need to sharpen a pencil
• Мне надо заточить карандаш = I need to sharpen a pencil

In many everyday contexts, they are interchangeable.

A rough tendency:

• надо can sound a little more conversational
• нужно can sound a little more neutral or formal

But in this sentence, both are natural.

Yes, but it means something slightly different.

• Мне нужно заточить карандаш = I need to sharpen the pencil
  This expresses necessity in a general sense.

• Я должен заточить карандаш = I must / am supposed to sharpen the pencil
  This can sound more like duty, obligation, or expectation.

So должен is stronger and often implies responsibility.

If you simply mean I need to, then мне нужно is usually the safer choice.

Russian does not have articles like a and the, so карандаш can mean either a pencil or the pencil.

You understand which one is meant from context.

So this sentence could be interpreted as:

• I need to sharpen a pencil before the lesson
• I need to sharpen the pencil before the lesson

Both are possible without more context.

Yes.

Урок often means:

• lesson
• class period
• sometimes school class

So перед уроком can naturally be translated as:

• before the lesson
• before class

The best English translation depends on context.

Then Russian would usually use the imperfective verb.

For example:

• Я точу карандаш. = I am sharpening the pencil.
• Мне нужно точить карандаши каждый день. = I need to sharpen pencils every day.

But in the original sentence, the speaker means one specific completed action before the lesson, so заточить is the right choice.

No. Точить / заточить can be used for sharpening various things, for example:

• заточить нож = sharpen a knife
• заточить карандаш = sharpen a pencil

However, with pencils, заточить карандаш is especially common and useful to learn as a set phrase.