На первой странице была красивая иллюстрация, а в конце книги — ещё одна.

In Russian, на странице is the normal way to say on a page. Russian treats a page as a surface, so на is used.

• на странице = on the page
• в книге = in the book

So:

• На первой странице = on the first page
• В конце книги = at the end of the book

English and Russian do not always choose the same preposition, so this is something you often just have to learn as a set phrase.

Because it agrees with странице.

After на in this meaning of location, страница goes into the prepositional case:

• nominative: первая страница
• prepositional: на первой странице

The adjective/ordinal первый must match the noun in:

• gender: feminine
• number: singular
• case: prepositional

So:

• первая → nominative feminine singular
• первой → prepositional feminine singular

Russian past tense agrees with the subject in gender and number.

The subject here is иллюстрация, which is feminine singular, so the past tense of быть is:

• был for masculine
• была for feminine
• было for neuter
• были for plural

So:

• иллюстрация была
• not иллюстрация был
• not иллюстрация было

They are both in the nominative feminine singular because иллюстрация is the subject of the clause, and красивая agrees with it.

Base form:

• красивая иллюстрация = a beautiful illustration

Agreement here is:

• feminine
• singular
• nominative

If the noun changed case, the adjective would change too:

• красивая иллюстрация
• красивой иллюстрации
• красивую иллюстрацию, etc.

Because конец often takes the genitive case to show the end of something.

So:

• конец книги = the end of the book
• в конце книги = at the end of the book

Here:

• конец is in the prepositional phrase в конце
• книги is genitive singular, dependent on конце

This pattern is very common:

• в начале фильма = at the beginning of the film
• в середине дня = in the middle of the day
• в конце книги = at the end of the book

А can often be translated as and, but it usually has a slight sense of contrast, switch of focus, or meanwhile/as for.

In this sentence, а connects two related facts:

• one illustration was on the first page,
• another was at the end of the book.

So it is not a strong contrast like but, but it is not the plainest and either. It feels like:

• and
• while
• whereas
• and then / and also in another place

A very literal feeling would be: On the first page there was..., and at the end of the book, another one.

The dash shows that something has been left out because it is understood from the first clause.

Full version:

• На первой странице была красивая иллюстрация, а в конце книги была ещё одна.

Russian often omits repeated words, especially была here, and uses a dash to mark the pause:

• ..., а в конце книги — ещё одна.

So the dash is standing in for the omitted была.

This is very natural Russian style and helps avoid repetition.

Here ещё одна means another one or one more.

• ещё = still / yet / more / else, depending on context
• одна = one, feminine

Because иллюстрация is feminine, the word for one is feminine too:

• masculine: один
• feminine: одна
• neuter: одно

So ещё одна really means one more [illustration].

Russian often leaves out the noun when it is obvious:

• ещё одна = one more one = another one

Even though иллюстрация is omitted in the second clause, it is still understood.

So одна must agree with the missing noun:

• implied noun: иллюстрация
• gender: feminine

That is why it is:

• ещё одна, not ещё один and not ещё одно

This is very common in Russian:

• У меня синяя ручка, а у тебя красная. The word ручка is omitted after красная, but the adjective still shows feminine agreement.

Russian word order is flexible. Starting with На первой странице puts the location/topic first.

That structure is very natural when introducing the existence of something somewhere:

• На первой странице была красивая иллюстрация. = On the first page there was a beautiful illustration.

If you say:

• Красивая иллюстрация была на первой странице, that sounds more like the beautiful illustration was on the first page—as if the illustration is already known and you are saying where it was.

So the original word order fits the idea of there was ... on the first page very well.

Yes. Russian often expresses there is/there was simply by putting a location first and then the noun phrase.

So:

• На первой странице была красивая иллюстрация literally looks like
• On the first page was a beautiful illustration

but in natural English it is usually:

• There was a beautiful illustration on the first page

Russian does not need a special dummy subject like English there.

Russian has no articles. It does not have separate words corresponding directly to English a/an and the.

Whether something is definite or indefinite is understood from:

• context
• word order
• shared knowledge
• intonation

So красивая иллюстрация could mean:

• a beautiful illustration
• the beautiful illustration

In this sentence, the natural interpretation is indefinite in English: a beautiful illustration, because it is being introduced for the first time.

Yes:

• На первой странице была красивая иллюстрация, а в конце книги была ещё одна.

This is grammatically correct. The version with the dash is simply more elegant and less repetitive.

So:

• with была = full and explicit
• with — = natural ellipsis, very common in writing

Both are correct, but the dash version sounds more polished.