Этот парень сказал, что придёт пораньше и купит билеты.

Because этот has to agree with парень in gender, number, and case.

• парень is masculine
• singular
• nominative case, because it is the subject of the sentence

So the correct form is этот = this for a masculine singular noun in the nominative.

Compare:

• этот парень = this guy
• эта девушка = this girl
• это место = this place
• эти люди = these people

Парень usually means guy, young man, or sometimes boyfriend depending on context.

In this sentence, it simply means guy or young man. So этот парень is a natural way to say this guy.

It is more informal and everyday than мужчина, which means man, or человек, which means person.

Because сказать and говорить are different in aspect and usage.

• сказать = to say, to tell; a completed act of saying
• говорить = to speak, to say in a more ongoing/general sense

Here, the sentence refers to one completed statement: the guy said something. So сказал is the natural choice.

Compare:

• Он сказал, что придёт. = He said he would come.
• Он говорил о поездке весь вечер. = He was talking about the trip all evening.

Что introduces the content of what was said. Here it means that.

So:

• Этот парень сказал, что... = This guy said that...

In English, that is often omitted:

• He said he would come earlier.

In Russian, что is normally kept in this kind of sentence.

Because they are perfective verbs, and perfective verbs do not have a true present tense in Russian. Their present-looking forms actually refer to the future.

So:

• прийти → придёт = he will come / he will arrive
• купить → купит = he will buy

This is a very important Russian pattern:

• imperfective future: будет покупать = will be buying
• perfective future: купит = will buy

In this sentence, the actions are seen as single completed events, so perfective forms are used.

Because the correct future form of прийти is придёт.

This verb is irregular and comes from the movement verb family related to идти. The stem changes, so the future forms are:

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

So придёт is just the standard correct form, even though it may not look predictable at first.

Пораньше means a bit earlier, somewhat earlier, or earlier than usual/expected.

It comes from раньше = earlier, sooner, and the prefix по- often softens it and gives the idea of a little or somewhat.

So:

• раньше = earlier
• пораньше = a little earlier / rather earlier

In this sentence, it suggests that he said he would come earlier than normal, earlier than planned, or simply fairly early.

Because Russian often leaves out subject pronouns when the subject is already clear.

In this sentence, the subject of both verbs is the same person:

• Этот парень сказал, что придёт пораньше и купит билеты.

The understood meaning is:

• ...что он придёт пораньше и он купит билеты

But repeating он would usually sound unnecessary. Russian prefers to omit it when the meaning is clear from context.

Because что придёт пораньше и купит билеты is a subordinate clause, and Russian normally separates subordinate clauses with a comma.

So:

• Этот парень сказал, что...

The comma marks the boundary between the main clause and the clause explaining what he said.

Because и connects two verbs inside the same subordinate clause, and both have the same understood subject.

• что придёт пораньше и купит билеты

Both actions belong to the same person:

• he will come earlier
• he will buy tickets

Since these are two coordinated predicates within one clause, no comma is needed before и.

Because the sentence talks about two complete future actions:

• he will arrive
• he will buy the tickets

Perfective aspect is commonly used for single, completed future events. It presents each action as a whole.

If imperfective were used instead, the meaning would shift toward process, repetition, or a less bounded action. For example:

• будет покупать would suggest will be buying or some kind of ongoing process

But here the idea is simple and result-oriented, so perfective is the natural choice.

Yes. Russian word order is flexible, although the version given is very natural and neutral:

• Этот парень сказал, что придёт пораньше и купит билеты.

You could change the order for emphasis, for example:

• Этот парень сказал, что билеты купит он.
  This emphasizes that he will buy the tickets.
• Пораньше придёт этот парень...
  This sounds marked and would only be used in a special context.

So the original order is the most straightforward, standard way to say it.

Yes. Билеты is the direct object of купит, so it is in the accusative case.

For plural inanimate nouns, the accusative often looks exactly like the nominative, and that is what happens here:

• nominative plural: билеты
• accusative plural: билеты

So even though the form does not change, the case is still accusative because of its role in the sentence.

Usually no, or at least not in normal standard Russian.

English can easily say:

• He said he would come earlier.

Russian normally keeps что:

• Он сказал, что придёт пораньше.

Omitting что would sound unnatural in most ordinary cases. So for learners, it is safest to include it.