Die Nahtzugabe gehört zur Änderungsarbeit.

Because Die Nahtzugabe is the subject of the sentence — the thing being talked about.

• Die Nahtzugabe = the seam allowance
• gehört = belongs / is part of
• zur Änderungsarbeit = to the alteration work

German main clauses normally put the conjugated verb in second position, so the structure is:

Die Nahtzugabe + gehört + zur Änderungsarbeit

Because Nahtzugabe is a feminine noun, so its nominative singular article is die.

A useful tip: in German, every noun has a grammatical gender, and you usually need to learn it together with the noun:

• die Nahtzugabe

Also, in compound nouns, the last part usually determines the gender. Here the final part is Zugabe, which is feminine, so the whole word is feminine too.

It is a compound noun:

• Naht = seam
• Zugabe = addition / extra amount / allowance

So Nahtzugabe literally means something like extra added for the seam, which is why the usual English term is seam allowance.

Here gehört is the 3rd person singular form of gehören.

In this sentence, gehören zu means:

• to belong to
• to be part of
• to be included in

So Die Nahtzugabe gehört zur Änderungsarbeit means that the seam allowance counts as part of the alteration work.

Important: this is not the verb hören (to hear), even though gehört can also be the past participle of hören in other contexts. Here it is clearly the present-tense verb gehören.

Zur is just the standard contraction of:

• zu + der = zur

So:

• zur Änderungsarbeit = zu der Änderungsarbeit

German often uses these contractions, and they are usually preferred in normal speech and writing.

Because zu is a preposition that takes the dative case.

Since Änderungsarbeit is feminine:

• nominative: die Änderungsarbeit
• dative: der Änderungsarbeit

So:

• zu der Änderungsarbeit
• contracted: zur Änderungsarbeit

It is in the dative singular because it follows zu.

You can see that from the article:

• nominative feminine: die
• dative feminine: der

So in the sentence:

• zur Änderungsarbeit = zu der Änderungsarbeit
• therefore Änderungsarbeit is dative singular

Änderungsarbeit is another compound noun:

• Änderung = alteration / change
• Arbeit = work

So Änderungsarbeit means alteration work.

The -s- between the two parts is a linking element (Fugen-s). It often appears in German compounds, but it does not have a separate meaning by itself.

So:

• Änderung + Arbeit → Änderungsarbeit

Learners usually just need to memorize compounds as whole words.

Yes, that would also be possible.

Compare:

• Die Nahtzugabe gehört zur Änderungsarbeit.
• Die Nahtzugabe ist Teil der Änderungsarbeit.

Both suggest that the seam allowance is included as part of the alteration work.

The difference is mostly stylistic:

• gehört zu = belongs to / is considered part of
• ist Teil von / der = is a part of

The original sentence sounds natural in a practical or technical context.

Because all nouns in German are capitalized.

So in this sentence:

• Nahtzugabe is a noun
• Änderungsarbeit is a noun

That is why they begin with capital letters.

A simple learner-friendly guide:

• Nahtzugabe ≈ naht-tsoo-GAH-buh
• Änderungsarbeit ≈ EN-de-rungs-ar-bite

A few notes:

• z in German is pronounced ts
• ä is often like e in bed or air, depending on accent
• g in Zugabe is a hard g
• ei in Arbeit sounds like English eye

The main stress is usually:

• NahtzuGAbe
• ÄNderungsarbeit

Yes. The vocabulary is fairly specialized.

• Nahtzugabe is a sewing/tailoring term
• Änderungsarbeit refers to alteration work, especially in clothing or textile contexts

So while the grammar is general German, the nouns themselves belong to a more technical or practical field.

Yes, that is a very good way to learn it.

gehören zu + dative is a common pattern meaning:

• to belong to
• to be part of
• to be included among

Examples:

• Das gehört zu meinem Job. = That belongs to / is part of my job.
• Geduld gehört zum Lernen. = Patience is part of learning.

So in your sentence, it is helpful to remember the pattern as:

etwas gehört zu etwas + dative

Yes, absolutely. It is a complete standard sentence with:

• a subject: Die Nahtzugabe
• a verb: gehört
• a prepositional phrase: zur Änderungsarbeit

So grammatically it is fully complete and natural.