В первом слоге слова слышна гласная, а потом идёт согласная.

В первом слоге uses the preposition в in the sense of in, so слог goes into the prepositional case:

• слог → в слоге
• первый → в первом

So:

• в = in
• первом = first (prepositional singular, masculine/neuter form)
• слоге = syllable (prepositional singular)

Together: in the first syllable.

Because слова is in the genitive case and means of the word.

Russian often expresses X of Y by putting Y in the genitive:

• слог слова = the syllable of the word
• в первом слоге слова = in the first syllable of the word

Here:

• слово = word
• слова = of the word

So слоге слова literally means syllable of the word.

Yes — historically, гласная is an adjective, but in modern Russian it is very commonly used as a noun meaning a vowel.

Similarly:

• гласная = vowel
• согласная = consonant

These are shortened noun-like uses of longer expressions such as:

• гласная буква = vowel letter
• гласный звук = vowel sound
• согласная буква = consonant letter
• согласный звук = consonant sound

In ordinary language, Russian speakers very often just say гласная and согласная.

Слышна is the short-form adjective from слышный, meaning audible / can be heard.

It agrees with гласная, which is feminine singular:

• masculine: слышен
• feminine: слышна
• neuter: слышно
• plural: слышны

So:

• гласная слышна = the vowel is audible / a vowel can be heard

Why not the others?

• слышно is usually impersonal: слышно шум or мне слышно = it is audible / I can hear
• слышится is a verb meaning is heard / seems to be heard, with a slightly different feel

Here слышна is a neat descriptive way to say that the vowel is what you hear in that position.

Both are possible. Russian word order is flexible.

• слышна гласная puts a bit more focus on what is heard
• гласная слышна can sound slightly more neutral or topic-first depending on context

In this sentence, слышна гласная fits the explanatory style well: first it says what is perceptible, then it continues with what comes next.

So this is more about information structure than strict grammar.

Yes, the basic meaning of идти / идёт is to go / is going, but Russian often uses it more broadly.

Here потом идёт согласная means something like:

• then a consonant follows
• then comes a consonant
• after that there is a consonant

So идёт is not literal physical movement here. It is being used to describe sequence.

This is very common in explanations of patterns, spelling, pronunciation, instructions, and descriptions.

The conjunction а often links two parts of a sentence and can signal:

• contrast
• transition
• change of focus
• simple sequencing with a slight and then / while / whereas feel

So:

• слышна гласная, а потом идёт согласная

means roughly:

• a vowel is heard, and then a consonant follows

The а makes the second part feel like the next step in the pattern. It is very natural in explanatory Russian.

In this sentence, it most naturally means a vowel sound, because the sentence says слышна — is heard.

You hear sounds, not letters. So the intended idea is probably:

• In the first syllable of the word, a vowel sound is heard, and then a consonant follows.

That said, Russian sometimes uses гласная and согласная a bit loosely, especially in classroom or grammar contexts, where sound and letter terminology can overlap in casual speech.

Russian has no articles like English a / an / the.

So гласная can mean:

• a vowel
• the vowel

and согласная can mean:

• a consonant
• the consonant

The exact meaning depends on context. In this sentence, English would usually say:

• a vowel
• a consonant

because it is describing a general pattern.

Because each adjective has to agree with the noun it belongs to.

• слог is masculine → первый слог
• in the prepositional case: в первом слоге

But:

• гласная is feminine
• согласная is feminine

That is why other agreeing words change accordingly:

• гласная слышна
• согласная as the following noun

So the sentence contains both masculine and feminine forms because it contains different nouns with different genders.

Yes. Depending on context, a Russian speaker might also say things like:

• В первом слоге слова слышится гласный звук, а потом идёт согласный.
• В первом слоге слова сначала слышна гласная, потом — согласная.
• В первом слоге слова сначала идёт гласная, а потом согласная.

The original sentence is grammatical and understandable, but in some contexts a speaker might prefer:

• сначала for clearer sequencing
• гласный звук / согласный звук for phonetic precision
• слышится instead of слышна if focusing more on the act of hearing

Most likely pronunciation, because of слышна — is heard.

If the focus were purely spelling or letter order, Russian might more naturally use wording like:

• В первом слоге слова стоит гласная, а потом согласная.
• В первом слоге слова сначала идёт гласная буква, а потом согласная.

So слышна strongly suggests that the sentence is about what you hear, not just what is written.

You could translate it literally that way word-for-word, but in natural English it is better as:

• then a consonant follows
• then comes a consonant
• after that there is a consonant

A very literal translation may help you see the structure, but it will not sound natural in English. This is one of those cases where Russian uses a motion verb in a broader, more abstract way than English usually does.