Zum einen ist der Hauptsatz kurz, zum anderen steht das Verb im Nebensatz am Ende.

It is a paired expression used to present two points.

Common English equivalents are:

• for one thing ... for another
• on the one hand ... on the other hand
• first ... second

So here it introduces two observations:

• Zum einen ist der Hauptsatz kurz
• zum anderen steht das Verb im Nebensatz am Ende

A useful thing to know is that zum einen ... zum anderen is quite common in written and careful spoken German.

Because zum einen takes the first position in the clause.

In German main clauses, the finite verb normally comes in second position. This is the famous V2 rule.

So the structure is:

• Zum einen = position 1
• ist = position 2
• der Hauptsatz = subject
• kurz = rest of the clause

That is why you get:

• Zum einen ist der Hauptsatz kurz.

If you removed zum einen, you would normally say:

• Der Hauptsatz ist kurz.

So the verb has not moved randomly; it is simply following the normal verb-second pattern.

For the same reason: zum anderen is in the first position, so the finite verb must come next.

Structure:

• Zum anderen = position 1
• steht = position 2
• das Verb = subject
• im Nebensatz am Ende = rest

Without zum anderen, the neutral order would be:

• Das Verb steht im Nebensatz am Ende.

So this is another example of normal German main-clause word order.

They are grammar terms:

• der Hauptsatz = main clause
• der Nebensatz = subordinate clause

A Hauptsatz can stand on its own as a complete sentence.

A Nebensatz usually depends on another clause and is often introduced by a subordinating conjunction such as:

• dass
• weil
• wenn
• obwohl

One key difference is word order:

• In a main clause, the finite verb is usually in second position.
• In a subordinate clause, the finite verb usually goes at the end.

That is exactly what the second half of the sentence is talking about.

Because they are nouns, and in German all nouns are capitalized.

So:

• der Hauptsatz
• der Nebensatz
• das Verb
• das Ende

This is one of the most visible differences from English spelling.

im is a contraction of in dem.

So:

• im Nebensatz = in dem Nebensatz

German often contracts certain preposition + article combinations:

• in dem → im
• an dem → am
• zu dem → zum
• zu der → zur

Here, in is used in a location sense: in the subordinate clause.
That is why German uses the dative here:

• dem Nebensatz

So im Nebensatz literally means in the subordinate clause.

am is a contraction of an dem.

So:

• am Ende = an dem Ende

In this expression, German idiomatically says am Ende for at the end.

This is just the standard way to say it:

• Das Verb steht am Ende. = The verb is at the end.

As with im, this is a very common contraction you should get used to seeing.

Because kurz here is a predicate adjective, not an adjective directly before a noun.

Compare:

• der kurze Hauptsatz = the short main clause
  
  • adjective before a noun, so it takes an ending
• der Hauptsatz ist kurz = the main clause is short
  
  • predicate adjective, so it has no ending

In your sentence:

• der Hauptsatz ist kurz

So kurz stays in its basic form.

German often uses stehen when talking about where words appear in a sentence or in a text.

So:

• Das Verb steht am Ende.

Literally this is The verb stands at the end, but in natural English we usually say:

• The verb comes at the end
• The verb is at the end

This use of stehen is very normal in grammar explanations and when describing written text.

It is mostly learned as a set pair, but there is some flexibility.

Very common forms are:

• zum einen ... zum anderen
• einerseits ... andererseits

These both present two contrasting or balancing points.

You will most often see zum einen paired with zum anderen.
Using only one half by itself is possible in some contexts, but learners should usually treat it as a pair.

Yes, the comma is correct here because the sentence links two main clauses:

• Zum einen ist der Hauptsatz kurz,
• zum anderen steht das Verb im Nebensatz am Ende.

In German, commas are commonly used to separate coordinated clauses like this, especially when the structure is clear and balanced.

So the comma helps show that the sentence consists of two parallel statements.

Yes. You could switch them if the context made that more natural:

• Zum einen steht das Verb im Nebensatz am Ende, zum anderen ist der Hauptsatz kurz.

That is grammatically fine.

What matters is that:

1. zum einen introduces one point
2. zum anderen introduces the other point
3. each clause still follows normal main-clause word order with the finite verb in second position

No. The whole sentence consists of two main clauses.

The phrase im Nebensatz just means in the subordinate clause. It is talking about a subordinate clause, not actually giving one.

So this is not a subordinate clause:

• zum anderen steht das Verb im Nebensatz am Ende

It is a normal main clause whose subject is das Verb.

A real subordinate clause would look more like:

• ..., weil das Verb im Nebensatz am Ende steht
• ..., dass das Verb im Nebensatz am Ende steht

There, the verb steht would actually move to the end of the subordinate clause.

If you remove the introductory expressions, you get:

• Der Hauptsatz ist kurz.
• Das Verb steht im Nebensatz am Ende.

That can help you see the structure more clearly.

Then the full sentence simply adds the paired connectors:

• Zum einen ist der Hauptsatz kurz,
• zum anderen steht das Verb im Nebensatz am Ende.

This is a useful strategy whenever German word order feels confusing: first find the simple core sentence, then add the introductory elements back in.