В слове «гора» первая буква — согласная, а вторая — гласная.

Because в means in here, so it takes the prepositional case for location.

• слово = dictionary form
• в слове = in the word

If в meant movement into, Russian would normally use the accusative instead, but that is not the meaning here.

Because the sentence is talking about the word гора as a word, not using it normally inside the sentence.

In Russian, when a word is being mentioned or analyzed, it is usually kept in its citation form, especially when it appears after слово:

• в слове гора
• в слове «гора»

So гора is not acting like an ordinary noun here; it is the object of discussion.

Those are standard Russian quotation marks, often called guillemets.

Here they show that гора is being mentioned as a word form, not used with its normal meaning. English does the same kind of thing when we write something like In the word “mountain”...

In Russian print, « » is very common and standard.

Because they go with буква, and буква is a feminine noun.

Russian ordinals behave like adjectives, so they must agree with the noun in:

• gender
• number
• case

So you get:

• первый звук = first sound
• первая буква = first letter
• первое слово = first word

Here they function like nouns meaning consonant and vowel.

Historically, they are adjective forms, but in modern Russian they are very commonly used on their own this way. You can think of them as short for:

• согласная буква
• гласная буква

Because the sentence is about буква, the feminine forms are used.

If the sentence were about звук (sound), you would normally get masculine forms:

• первый звук — согласный
• второй — гласный

Russian usually leaves out the present-tense verb to be in sentences like this.

So:

• первая буква — согласная

literally has no written word for is, but it means the first letter is a consonant.

This is completely normal in Russian.

The dash marks the place where English would use is.

It is very common in Russian sentences where one thing is identified as another thing:

• Москва — столица России.
• Первая буква — согласная.

Here the dash helps separate the subject from what is being said about it. In speech, there is often a slight pause there too.

Because а often connects two ideas with a slight contrast or comparison.

Here the sentence is comparing the first letter with the second:

• the first is one kind,
• а the second is another kind.

So а here is like whereas / while / and on the other hand.

If you used и, it would sound more like simple addition, with less contrast.

Because Russian often omits words that are already obvious from the context.

So:

• а вторая — гласная

really means:

• а вторая буква — гласная

Both are correct, but the shorter version sounds more natural because буква has already been mentioned.

It is talking about letters, because it explicitly says буква.

That matters in Russian, because:

• буква = letter
• звук = sound

The words согласная and гласная can be used for either letters or sounds, so the noun around them tells you which meaning is intended. Here it is clearly about letters.

Russian has no words exactly like English a and the.

Instead, definiteness is understood from context. In this sentence, первая буква naturally means the first letter, because we are talking about a specific word, гора.

So Russian does not need an article here; the meaning is still clear.

Yes. Russian word order is fairly flexible.

For example, this is also natural:

• Первая буква в слове «гора» — согласная, а вторая — гласная.

The version with В слове «гора» first puts the setting up front: as for the word гора. That is often a very natural way to introduce what you are analyzing.

So the word order choice is mostly about emphasis and information flow, not basic meaning.