Learn Hardcore German: Abends ist es für mich entspannend, ein paar Seiten in diesem Fachbuch zu lesen. - In the evening it is relaxing for me to read a few pages in this textbook.

but am Abend is more like “in the evening (on a given day / on that evening)”, i.e. more specific, less clearly habitual. In everyday speech, abends is more natural when you mean a regular routine.

Why is Abends capitalized? Is it a noun here?

It’s capitalized simply because it is the first word of the sentence.

If it appeared in the middle of a sentence, it would normally be:

Ich lese abends ein paar Seiten.

So here abends is an adverb (not a noun), and the capital A in Abends is just normal sentence-initial capitalization, not a grammatical marker.

What does es refer to in ist es für mich entspannend? Is it necessary?

Here es is a dummy subject (also called “placeholder es” / Scheinesubjekt). It doesn’t have concrete meaning by itself.

The real logical subject of the sentence is the infinitive clause:

ein paar Seiten in diesem Fachbuch zu lesen

German often moves such long “subject clauses” to the end and puts es in the subject position:

Abends ist es für mich entspannend, ein paar Seiten in diesem Fachbuch zu lesen.

Literally: In the evenings it is relaxing for me, to read a few pages in this textbook.

You cannot just leave out es here:

❌ Abends ist für mich entspannend, ein paar Seiten … zu lesen. (sounds wrong)
✅ Abends ist es für mich entspannend, ein paar Seiten … zu lesen.

Can I change the word order, like Es ist für mich abends entspannend … or Für mich ist es abends entspannend …?

Yes, several word orders are possible and natural, as long as the finite verb (ist) stays in second position in the main clause:

Abends ist es für mich entspannend, …
Es ist für mich abends entspannend, …
Für mich ist es abends entspannend, …

All three are grammatically correct. They just differ slightly in emphasis:

Starting with Abends emphasizes when.
Starting with Für mich emphasizes for whom.
Starting with Es is more neutral / default.

The meaning remains essentially the same.

Why is it für mich and not für mir?

Because the preposition für always takes the accusative case in German.

Pronouns:

ich → mich (accusative)
ich → mir (dative)

After für, you must use the accusative:

für mich (for me)
für dich
für ihn / sie / es
für uns, etc.

So für mir is always incorrect; it must be für mich.

What is the difference between entspannend and entspannt here? Could I say ist es für mich entspannt?

In this sentence, entspannend is a present participle used like an adjective meaning:

entspannend = relaxing (causing relaxation)

So:

Es ist für mich entspannend, … = It is relaxing for me to…

Entspannt is the adjective meaning:

entspannt = relaxed (in a relaxed state)

So:

Ich bin entspannt. = I am relaxed.

In your sentence, you want to describe the activity as something that causes relaxation, so entspannend is correct.

Es ist für mich entspannt, … sounds wrong or at least very unusual in standard German in this context. Use entspannend.

Why is there a comma before ein paar Seiten in diesem Fachbuch zu lesen?

The part ein paar Seiten in diesem Fachbuch zu lesen is a zu-infinitive clause (“to read a few pages in this textbook”) that functions as the real subject of the sentence.

According to modern German punctuation rules:

A comma can often be used before zu-infinitive groups.
It becomes obligatory when the infinitive group is related to a corresponding word in the main clause, such as es, darauf, daran, etc.

Here es is that corresponding word (Korrelat), so the comma before the infinitive group is required:

… ist es für mich entspannend, ein paar Seiten … zu lesen.

Leaving the comma out here would be considered a spelling error.

Why do we use zu lesen and not just lesen?

German normally uses zu + infinitive when an infinitive clause (like an English “to do something” clause) functions as:

Subject
Object
Or is dependent on an adjective or noun

Here, zu lesen belongs to the infinitive group functioning as the subject:

ein paar Seiten in diesem Fachbuch zu lesen = to read a few pages in this textbook

Without zu, it would be interpreted more like a finite verb needing a subject, which is not what we want:

❌ …, ein paar Seiten … lesen. (in this structure, wrong)
✅ …, ein paar Seiten … zu lesen.

So zu is part of the German infinitive construction that corresponds to English “to read”.

What does ein paar Seiten mean exactly? How is it different from einige Seiten?

Both mean roughly “a few pages”, but there is a nuance:

ein paar Seiten
- Very common in spoken language
- Often a bit vague and informal
- Roughly “a couple of / a few pages” (not many, but not very precise)
einige Seiten
- Slightly more formal / neutral
- Can sometimes feel like “quite a few”, depending on context
- Still “some pages” or “several pages”

In everyday speech, ein paar Seiten is the most natural choice here to express a small, relaxed amount of reading.

Why is it in diesem Fachbuch and not in dieses Fachbuch?

The preposition in can take either:

dative (for location: where?), or
accusative (for direction: where to?).

Here, you are not moving into the book; you are talking about reading inside it (location).

So you use dative:

in diesem Fachbuch (in + dative singular, neuter: dem Buch → diesem Buch)
Full phrase: ein paar Seiten in diesem Fachbuch = a few pages in this textbook

If it were about movement into something (e.g. go into the room), you would use accusative:

Ich gehe in dieses Zimmer. (direction: into this room)

Could I also say aus diesem Fachbuch instead of in diesem Fachbuch? What’s the difference?

Yes, grammatically you can say both, but they have slightly different nuances:

ein paar Seiten in diesem Fachbuch lesen
- Focuses more on the place/content: pages within this book
- Neutral, very common for describing what you’re reading in general
ein paar Seiten aus diesem Fachbuch lesen
- Emphasizes more that you are taking text from this book (e.g. reading aloud from it, or using it as a source)
- Slight feeling of “from this source”

In your sentence, where you describe a quiet, personal habit, in diesem Fachbuch fits perfectly and sounds very natural.

Could I rephrase this as Abends entspanne ich mich, indem ich ein paar Seiten in diesem Fachbuch lese? Is that equivalent?

Yes, that is a good and natural alternative:

Abends entspanne ich mich, indem ich ein paar Seiten in diesem Fachbuch lese.
- Literally: In the evenings I relax by reading a few pages in this textbook.

Differences:

Original:
Abends ist es für mich entspannend, ein paar Seiten in diesem Fachbuch zu lesen.
→ Focus on the activity being relaxing.
Alternative:
Abends entspanne ich mich, indem ich …
→ Focus on you and the fact that you relax, and how you do it.

Both are perfectly correct; they just structure the idea differently.