Поиск начался утром.

Because поиск is the subject of the sentence, so it appears in the nominative case.

In this sentence, Russian is structured like:

• поиск = the search
• начался = began
• утром = in the morning

So literally, it is The search began in the morning.

In the past tense, Russian verbs agree with the subject in gender and number.

Since поиск is masculine singular, the verb must be начался.

Compare:

• поиск начался — the search began
• операция началась — the operation began
• расследование началось — the investigation began
• поиски начались — the searches / search efforts began

Here, -ся is part of the verb начаться, which means to begin.

This is different from начать, which usually means to start something.

Compare:

• Они начали поиск. — They started the search.
• Поиск начался. — The search began.

So in this sentence, -ся does not mean a literal reflexive idea like it began itself in natural English. It is just part of the verb form that makes the verb work as an intransitive verb: the event begins, rather than someone starting it directly.

Начаться is the perfective verb, and начался presents the beginning as a single completed event: at some point, the search began.

That fits well with a sentence like this, especially when a specific time is given.

Начинался would be imperfective and would usually suggest a process, repeated action, background description, or something like was beginning / used to begin depending on context.

Compare:

• Поиск начался утром. — The search began in the morning.
  (one completed start)

• Поиск начинался утром каждый день. — The search used to begin in the morning every day.
  (repeated/habitual)

No. In modern Russian, the past tense is normally formed without a separate word meaning was.

So:

• начался already means began
• you do not add был here

Using был with another past-tense verb is possible only in special meanings and is not what you want in a basic sentence like this.

Утром is the instrumental singular form of утро (morning).

So:

• утро — morning
• утром — in the morning

This is a very common Russian pattern with parts of the day.

Russian often uses the instrumental case without a preposition for certain time expressions, especially with parts of the day.

So you get:

• утром — in the morning
• днём — in the daytime / during the day
• вечером — in the evening
• ночью — at night

This is just a standard idiomatic pattern. English uses a preposition here, but Russian often does not.

Grammatically, it is the instrumental form of the noun утро, but in the sentence it functions adverbially, meaning it tells you when the action happened.

So it is useful to think of it as:

• formally: a noun form
• functionally: an adverb-like time expression

Russian does this quite often.

Because Russian has no articles like a, an, or the.

Russian leaves definiteness to context.

So поиск can correspond to:

• the search
• a search

In this sentence, English would normally say the search, but Russian does not need a separate word for that.

Yes. Russian word order is much more flexible than English word order, because the case endings and verb forms already show the grammatical relationships.

The sentence Поиск начался утром is a neutral, natural order.

Other orders are possible, but the emphasis changes:

• Поиск начался утром. — neutral
• Утром начался поиск. — emphasizes in the morning
• Начался поиск утром. — possible, but more marked or stylistic

So the basic meaning stays similar, but the information focus shifts.

No. Then you would usually use the transitive verb начать instead of начаться.

For example:

• Они начали поиск утром. — They started the search in the morning.

That is different from:

• Поиск начался утром. — The search began in the morning.

So Russian makes the same kind of distinction English does:

• someone started something
• something began

Yes, it is completely natural.

It is a simple, standard Russian sentence with:

• a subject in the nominative: поиск
• a past-tense verb agreeing with that subject: начался
• a time expression: утром

So for a learner, it is a very good model sentence for noticing several common Russian patterns at once.