Die Versandkosten betragen fünf Euro.

German very often combines nouns into a single compound word.

• Versand = shipping / dispatch
• Kosten = costs

So Versandkosten literally means shipping costs.

A useful rule: in German compounds, the last part is the main noun. That is why the whole word is treated grammatically like Kosten.

Because Versandkosten is plural here.

In German, the definite article for plural nouns in the nominative is die:

• die Kosten = the costs
• die Versandkosten = the shipping costs

In this sentence, Die Versandkosten is the subject, so it is in the nominative plural.

That is normal in German. Kosten is very commonly used in the plural, even when talking about one total amount someone has to pay.

So German prefers:

• Die Versandkosten betragen fünf Euro.

rather than trying to make shipping cost singular.

If you want a singular idea, German usually switches to a different noun, for example:

• Der Versand kostet fünf Euro.
• Die Versandgebühr beträgt fünf Euro.

Betragen here means to amount to or to come to.

So:

• Die Versandkosten betragen fünf Euro. = The shipping costs amount to five euros.

It is a common and fairly neutral/formal verb for prices, totals, distances, percentages, and similar amounts.

Examples:

• Die Miete beträgt 800 Euro.
• Die Entfernung beträgt 20 Kilometer.

Because betragen is especially natural when giving an exact amount.

• Die Versandkosten betragen fünf Euro. = very natural
• Der Versand kostet fünf Euro. = also very natural
• Die Versandkosten sind fünf Euro. = understandable, but less idiomatic

So betragen is a good choice when you want a precise, matter-of-fact statement.

It is the accusative, because betragen takes a direct object.

So in this sentence:

• Die Versandkosten = subject
• betragen = verb
• fünf Euro = accusative object

With fünf Euro, you do not see a special ending, so nominative and accusative look the same here.

You can see the case more clearly in the singular:

• Die Versandkosten betragen einen Euro.

Here einen Euro clearly shows the accusative.

In standard German, the plural of Euro is usually just Euro after numbers.

So:

• ein Euro
• zwei Euro
• fünf Euro

German does not normally add -s here.

Because German main clauses normally follow the verb-second rule.

In this sentence:

1. Die Versandkosten
2. betragen
3. fünf Euro

The finite verb betragen must come in the second position.

This is one of the most important word-order rules in German.

Because all nouns are capitalized in German.

So in this sentence:

• Versandkosten is a noun
• Euro is a noun

That is why both start with a capital letter. This is a standard spelling rule in German.