Извините, поезд задерживается, поэтому я приду позже.

Извините means sorry, excuse me, or forgive me depending on context.

In this sentence, it works like Sorry... at the beginning of an explanation.

It is the formal or plural imperative form of извинить. Russian uses the same form:

• when speaking politely to one person
• when speaking to more than one person

So:

• Извини = informal, to one person you know well
• Извините = polite/formal, or plural

Russian often uses Извините where English would simply say Sorry.

A more literal I am sorry structure also exists, for example:

• Мне жаль = I am sorry / I feel sorry
• Прошу прощения = I beg your pardon / sorry

But Извините is extremely common in everyday speech when apologizing before giving a reason:

• Извините, я опоздаю.
• Извините, я не смогу прийти.

So this sentence sounds very natural.

Поезд is in the nominative case because it is the subject of the verb задерживается.

So in this sentence:

• поезд = the train
• it is the thing that is being delayed

The basic dictionary form is also поезд, so nothing changes here.

Russian often expresses this idea with the verb задерживаться, which literally has a reflexive ending -ся.

Here, поезд задерживается means:

• the train is being delayed
• or more naturally, the train is delayed

English often uses a passive structure: is delayed. Russian often prefers this reflexive/middle-style construction instead of a direct passive.

So although the grammar is different, the meaning matches very well.

The -ся ending often gives a verb a reflexive, passive-like, or middle meaning.

Here it helps create the sense that the delay is happening to the train:

• задерживать = to delay something
• задерживаться = to be delayed / to get delayed

Compare:

• Они задерживают поезд. = They are delaying the train.
• Поезд задерживается. = The train is delayed / is being delayed.

So -ся is important here.

Поэтому means therefore, so, or for that reason.

It introduces the result of what was just said:

• поезд задерживается = the train is delayed
• поэтому я приду позже = therefore / so I will come later

A very common learner mistake is confusing поэтому with потому что:

• поэтому = so / therefore
• потому что = because

So:

• Поезд задерживается, поэтому я приду позже. = The train is delayed, so I’ll come later.
• Я приду позже, потому что поезд задерживается. = I’ll come later because the train is delayed.

There is a comma because the sentence contains two clauses:

• поезд задерживается
• поэтому я приду позже

In Russian, clauses like these are normally separated by a comma, especially when connected by words like поэтому.

So the punctuation here is standard.

Приду is the future tense of the perfective verb прийти.

Russian has two aspects:

• imperfective: process, repetition, ongoing action
• perfective: single completed result

Here the speaker means a single future arrival:

• I will arrive / come later

That is why Russian uses the perfective future:

• приду

By contrast:

• приходить is imperfective
• буду приходить would mean I will be coming or I will come repeatedly, which does not fit here

So я приду позже is the natural choice.

This is just an irregular verb pattern that learners need to memorize.

The infinitive is прийти = to come, to arrive.

Its future forms are:

• я приду
• ты придёшь
• он / она придёт
• мы придём
• вы придёте
• они придут

So приду may not look very close to прийти, but it is the correct future form.

Позже means later. Поздно means late.

That difference matters:

• Я приду позже. = I’ll come later.
• Я приду поздно. = I’ll come late.

In this sentence, the idea is usually later than expected, so позже is the best choice.

Also, позже is the comparative form:

• поздно = late
• позже = later

Yes, sometimes, but the nuance is a little different.

• Поезд задерживается = the train is delayed
• Поезд опаздывает = the train is late / running late

In many situations, both could work.

A rough difference:

• задерживается focuses on the delay itself
• опаздывает focuses on being behind schedule

In announcements and travel contexts, задерживается is very common.

Yes, Russian can often omit subject pronouns when the verb already makes the subject clear.

So both are possible:

• я приду позже
• приду позже

Because приду clearly means I will come, the pronoun is not strictly necessary.

But including я can make the sentence:

• clearer
• slightly more explicit
• a bit more natural in contrastive or explanatory speech

So the version with я is completely normal.

Russian word order is fairly flexible, though not random.

This version is neutral:

• Извините, поезд задерживается, поэтому я приду позже.

Other versions are possible, for example:

• Извините, поезд задерживается, поэтому приду позже.
• Извините, поэтому я приду позже: поезд задерживается.
• Я приду позже, потому что поезд задерживается.

Changing the word order can affect emphasis, but the original sentence is a very natural standard way to say it.

If you are speaking to a friend, you would usually say:

• Извини, поезд задерживается, поэтому я приду позже.

The only change is:

• Извините → Извини

Everything else can stay the same.