Согласование границ началось утром.

Because the subject is согласование, and согласование is a neuter singular noun.

In Russian past tense, the verb agrees with the subject in gender and number:

• начался = masculine singular
• началась = feminine singular
• началось = neuter singular
• начались = plural

So:

• Согласование ... началось = The coordination/agreement ... began

If the subject were работа (feminine), you would get работа началась.

Границ is genitive plural of граница.

The basic noun is:

• граница = border, boundary

Its genitive plural form is:

• границ = of borders / of boundaries

In согласование границ, the noun согласование is a verbal noun meaning something like coordination, agreement, or settling, and the thing being coordinated/agreed upon is often put in the genitive.

So:

• согласование границ = the coordination/settling of borders

This is very common in Russian with abstract nouns derived from verbs.

Because границы would usually be nominative plural or accusative plural, not the form needed after согласование here.

The pattern is:

• согласование чего? = coordination/agreement of what?

That question чего? calls for the genitive case.

So:

• singular: согласование границы = coordination of a border
• plural: согласование границ = coordination of borders

Since the sentence is talking about borders in general or multiple borders, Russian uses genitive plural: границ.

Согласование is a noun formed from the verb согласовать / согласовывать.

Depending on context, it can mean:

• coordination
• agreement
• approval
• harmonization
• settling or working out

In this sentence, it likely means something like:

• the process of agreeing on borders
• the coordination/settlement of borders
• the approval of borders

The exact English word depends on the broader context, but grammatically it is a noun, not a verb.

Началось is past tense of the verb начаться.

More specifically:

• начаться = perfective
• началось = it began / it started

Because it is perfective, it presents the beginning as a completed event: the action of starting happened.

Compare:

• начиналось = was beginning / used to begin / began (imperfective, more process-oriented)
• началось = began, started (perfective, focuses on the event of starting)

In this sentence, началось is the natural choice because the sentence states that the process started in the morning.

The dictionary form here is начаться, which is the reflexive form of начать.

Compare:

• начать что-то = to start something
• начаться = to begin, to start

So:

• Они начали переговоры = They started the negotiations.
• Переговоры начались = The negotiations began.

In your sentence, согласование границ is not doing the action of starting something else; rather, it itself began. That is why Russian uses начаться:

• Согласование границ началось утром.

The -ся / -сь here often makes the verb intransitive: to begin rather than to start something.

Утром is the instrumental case of утро.

Russian often uses certain time expressions in the instrumental to mean at/in a certain part of the day:

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

So in this sentence:

• началось утром = began in the morning

This is a fixed and very common adverbial use of the instrumental case.

Yes. Russian word order is flexible, and the meaning would stay basically the same, though the emphasis can change.

For example:

• Согласование границ началось утром.
  Neutral: the topic is the border agreement/coordination.

• Утром началось согласование границ.
  Emphasis first on when it began.

• Началось утром согласование границ.
  Less neutral, more stylistic or contextual.

Russian often uses word order to manage focus and information structure, not just grammar.

Yes. The whole phrase согласование границ functions as the subject.

The head of that subject is согласование, and границ depends on it.

So structurally:

• согласование = main noun of the subject
• границ = dependent genitive noun
• началось = predicate verb
• утром = adverbial time expression

A rough structure is:

• [The coordination of borders] [began] [in the morning].

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

So Согласование границ началось утром could correspond in English to:

• The border settlement began in the morning
• A border settlement began in the morning
• Border coordination began in the morning

Which English article sounds best depends on context, but Russian does not mark that distinction with a separate word.

A natural pronunciation is:

• Согласовáние гранИц началóсь ýтром.

Stress:

• согласовáние
• грани́ц
• начало́сь
• у́тром

A rough English-style approximation:

• suh-gluh-suh-VAH-nee-yeh grah-NEETS nuh-chuh-LOHS OO-trum

A couple of points:

• г is a hard g sound, like in go
• ц sounds like ts
• unstressed о often sounds closer to a in actual speech

Yes. Граница can mean:

• a physical border
• a boundary
• a limit

So согласование границ could refer to:

• state borders
• administrative boundaries
• property boundaries
• conceptual limits, depending on context

Russian leaves that open unless the wider context specifies it.