El segundo capítulo de esta novela es más interesante.

El is the masculine singular definite article, meaning the.

It is used because capítulo is a masculine singular noun: el capítulo.
So El segundo capítulo means the second chapter.

Spanish usually uses the definite article in places where English also uses the, especially when talking about a specific thing.

In modern everyday Spanish, ordinal numbers like primero, segundo, tercero usually come before the noun:

• el segundo capítulo
• la primera vez
• el tercer día

You may sometimes see capítulo segundo, especially in formal, literary, legal, or old-fashioned styles, but segundo capítulo is the normal order for most learners to use.

Because segundo is describing capítulo, and capítulo is masculine.

Adjectives and ordinal numbers in Spanish usually agree with the noun they describe:

• el segundo capítulo → masculine singular
• la segunda novela → feminine singular
• los segundos capítulos → masculine plural
• las segundas novelas → feminine plural

So the form depends on the noun, not on the speaker’s opinion or the meaning in English.

Because novela is a feminine singular noun, so the demonstrative must also be feminine singular.

The forms are:

• este → masculine singular
• esta → feminine singular
• estos → masculine plural
• estas → feminine plural

So:

• este capítulo
• esta novela

Even though chapter is masculine, novela is feminine, so it must be esta novela.

Here de shows a relationship like of in English:

• el segundo capítulo de esta novela
  = the second chapter of this novel

It links capítulo to novela and tells you which chapter we are talking about.

This is a very common structure in Spanish:

• el final de la película
• la portada del libro
• el nombre de la ciudad

Spanish has two verbs for to be: ser and estar.

Here it is es because interesting is describing an essential quality or characteristic of the chapter, not a temporary state or location.

So:

• El capítulo es interesante = the chapter is interesting
• La novela es larga = the novel is long

You would not normally use estar with interesante in this sentence.

Más + adjective means more + adjective.

So:

• más interesante = more interesting
• más largo = longer / more long
• más difícil = more difficult

This is the regular comparative pattern in Spanish:

• más + adjective
• más + adverb
• más + noun

In your sentence, más interesante means the chapter has a higher degree of interest.

Because this sentence is making an incomplete comparison: it says the chapter is more interesting, but it does not say than what.

If you want to say more interesting than the first chapter, Spanish uses que for than:

• El segundo capítulo es más interesante que el primero.

So:

• más interesante = more interesting
• más interesante que... = more interesting than...

Because interesante is an adjective that has the same form for masculine and feminine in the singular.

Compare:

• un capítulo interesante
• una novela interesante

The adjective only changes in the plural:

• capítulos interesantes
• novelas interesantes

Many Spanish adjectives ending in -e work like this:

• interesante
• importante
• difícil (also same for masculine/feminine)

This is a very common learner question.

• interesante = interesting
• interesado / interesada = interested

So:

• El capítulo es interesante. = The chapter is interesting.
• Estoy interesado en la novela. = I am interested in the novel.

In your sentence, the chapter causes interest, so it must be interesante, not interesado.

Yes, but the meaning becomes less specific.

• de esta novela = of this novel
• de la novela = of the novel

Use esta when you want to point to a particular novel, like this one.
Without esta, it is still grammatical, but it sounds less explicitly demonstrative.

So both are correct, but they are not exactly the same in meaning.

A little, but the original order is the most natural.

Normal order:

• El segundo capítulo de esta novela es más interesante.

You can move parts around for emphasis, but that usually sounds more marked or literary. For example:

• Más interesante es el segundo capítulo de esta novela.
  This is grammatical, but much less neutral.

For everyday Spanish, stick with the standard order: subject + verb + comparative adjective.