Learn Hardcore French: Certains lisent ce roman, d'autres préfèrent la série. - Some read this novel, others prefer the series.

Certains here is an indefinite pronoun meaning “some (people)”.
The noun “people” is understood from context, so French doesn’t repeat it: Certains lisent… literally “Some read…”.
You could add a noun (e.g. Certains étudiants lisent ce roman – “Some students read this novel”), but when the group is already clear, Certains alone is natural.

What is the difference between certains and words like quelques or quelques-uns?

certains (as in the sentence) is a pronoun: it stands alone – Certains lisent… = “Some (people) read…”.
quelques is a determiner: it must be followed by a noun – Quelques élèves lisent ce roman = “Some students read this novel”.
quelques-uns is also a pronoun, similar to certains, but a bit more informal or concrete: Quelques-uns lisent ce roman ≈ “Some (of them) read this novel.”
In this sentence, Certains… d'autres… is the most idiomatic pattern: “Some…, others…”.

What exactly does d'autres mean, and why is there an apostrophe?

d'autres = de + autres, with elision of the e in de before a vowel (a in autres), hence the apostrophe: d'.
It means “others” in a partitive sense: certains …, d'autres … = “some…, others… (of them)”.
If you say les autres, you’re referring to all the remaining people:

Certains lisent ce roman, les autres préfèrent la série. = “Some read this novel, the rest prefer the series.”

Why are the verbs plural: lisent and préfèrent?

Both subjects, Certains and d'autres, refer to more than one person, so they are third person plural.
Therefore their verbs must also be in the third person plural:

ils lisent → Certains lisent
ils préfèrent → d'autres préfèrent
Using the singular (e.g. lit, préfère) would be ungrammatical here.

Why is it ce roman but la série? Why different articles?

ce roman uses the demonstrative ce (“this/that”) → it points to a specific novel, often one already mentioned, shown, or strongly in focus.
la série uses the definite article la (“the”) → it also refers to a specific series, but more as a known thing in general, not something you are “pointing at” in the same way.
You could also say cette série (“this series”) if you want to put symmetrical emphasis on the series too: Certains lisent ce roman, d'autres préfèrent cette série.

Does Certains have a feminine form? What if I’m talking only about women?

Yes.

Certains (with -s) is masculine plural: “some (men / mixed group)”.
Certaines (with -es) is feminine plural: “some (women)”.
So for only women, you’d say: Certaines lisent ce roman, d'autres préfèrent la série.

What is the difference between roman and livre in French?

un roman = specifically a novel (a long fictional narrative).
un livre = a book in general (could be a novel, a textbook, a cookbook, etc.).
So this sentence is explicitly contrasting a particular novel with its series adaptation, not just any book.

Is série here necessarily a TV series, or can it be other kinds of series?

By default in modern usage, la série often suggests a TV series (or a streaming series).
However, context decides: it could also be a comic-book series, a book series, or another serial format.
Without extra context, many listeners would assume a TV/streaming series adapted from the novel.

How is préfèrent formed, and why is there an accent change compared to the infinitive préférer?

The infinitive is préférer. In the present tense, some forms change the position of the stress and thus the accents:

je préfère, tu préfères, il/elle préfère, ils/elles préfèrent
but nous préférons, vous préférez
In d'autres préfèrent, the subject is ils (understood), so we use préfèrent (3rd person plural), with è (grave accent) in the stressed syllable.

How do you pronounce Certains lisent ce roman, d'autres préfèrent la série? Are there any important liaisons?

Key points:

Certains ≈ ser-tin (nasal -in); in careful speech there is a liaison: certains‿lisent → the final s sounds like z.
lisent: the final -ent is silent → liz.
d'autres: dotr (the d' links directly to autres).
préfèrent: final -ent is silent → pré-fèr.
la série: la sé-rie, with é like in English say.
So a smooth version is roughly: ser-tin‿lizt sə ro-man, dotr pré-fèr la sé-rie.