Merkelappen er på plagget.

In Norwegian, the definite article is usually added to the end of the noun instead of being a separate word before it.

• merkelapp = label / tag
• merkelappen = the label / the tag
• plagg = garment
• plagget = the garment

So:

• -en is a common definite ending
• -et is a neuter definite ending

This is one of the biggest differences from English.

The dictionary forms are:

• en merkelapp = a label / a tag
• et plagg = a garment

Their genders are:

• merkelapp: common gender
• plagg: neuter

That is why the definite forms are different:

• merkelapp → merkelappen
• plagg → plagget

Because the sentence refers to a specific label and a specific garment.

• Merkelappen = the label
• plagget = the garment

This is very natural if both are already known from the context, for example if someone is looking at one particular piece of clothing.

If you wanted a more general or indefinite meaning, you would use forms like:

• en merkelapp
• et plagg

Here på means on or attached to.

So på plagget means the label is on the garment.

Using i would usually mean in or inside. That would change the meaning:

• på plagget = on the garment / attached to it
• i plagget = in the garment / inside it

For a tag or label physically attached to clothing, på is the normal choice in this sentence.

Yes. Er is the present tense of å være = to be.

So:

• jeg er = I am
• du er = you are
• han/hun er = he/she is
• de er = they are

Unlike English, Norwegian does not change the present form depending on the subject. It is always er.

Yes, in this sentence it is very similar to English:

• Merkelappen = subject
• er = verb
• på plagget = prepositional phrase

So the pattern is:

subject + verb + place/location

However, Norwegian main clauses follow the V2 rule, which means the verb normally stays in the second position. If you move på plagget to the front for emphasis, you get:

• På plagget er merkelappen.

That is possible, but it sounds more marked or literary. The original sentence is the most straightforward order.

Merkelappen er på plagget is grammatical and easy to understand.

But in everyday Norwegian, if you want to emphasize that something is physically attached or positioned somewhere, people often use verbs like:

• sitter = sits / is attached
• sometimes henger = hangs

So a very natural alternative is:

• Merkelappen sitter på plagget.

That can sound a bit more idiomatic than er when talking about a label attached to clothing.

You would use the indefinite forms:

• en merkelapp = a label
• et plagg = a garment

So the sentence would become:

• En merkelapp er på et plagg.

That is grammatically correct, but it may sound a little unnatural in ordinary speech because it is very generic.

In real-life Norwegian, people would often choose a different structure, depending on the situation, for example:

• Det er en merkelapp på plagget. = There is a label on the garment.
• En merkelapp sitter på plagget. = A label is attached to the garment.

Yes, both can be used, but they are not always identical in tone.

• merkelapp often suggests a tag, label, or something used for marking
• etikett often means label in a product/package sense, and can also mean etiquette in another context

For clothing, merkelapp works well for a tag or identifying label. In some contexts, etikett may also be possible, but merkelapp is a very good choice here.