Stålet er sterkt.

Because -et is the definite ending for many neuter nouns in Norwegian.

• et stål = a steel / steel (indefinite form, though this is not always the most natural way to use the word)
• stålet = the steel (definite form)

So stålet means the steel.

Norwegian often puts the definite article at the end of the noun instead of using a separate word like English the.

Because the adjective agrees with the noun.

Stål is a neuter noun, and when an adjective describes a singular neuter noun after a verb like er (is), the adjective usually takes -t:

• en sterk mann = a strong man
• ei/en sterk kvinne = a strong woman
• et sterkt materiale = a strong material

So:

• Stålet er sterkt. = The steel is strong.

This is called adjective agreement.

You learn it together with the noun article:

• et stål

In practice, learners usually memorize nouns as:

• en bil
• ei bok
• et hus
• et stål

That article tells you the grammatical gender, which then affects adjective forms and definite forms.

For this sentence, the important result is:

• et stål → neuter
• therefore sterkt, not sterk

Because Norwegian usually expresses definiteness by adding an ending to the noun.

So instead of:

• the steel

Norwegian commonly says:

• stålet

The ending does the job of the.

Very roughly:

• stål = steel
• stålet = the steel

Yes, but it means something a little different.

• Stål er sterkt. = Steel is strong.
  This is a general statement about steel as a material.

• Stålet er sterkt. = The steel is strong.
  This refers to specific steel already known from the context.

So the difference is mainly:

• stål = steel in general
• stålet = the specific steel

Er means is. It is the present tense of å være (to be).

So the sentence structure is:

• Stålet = the steel
• er = is
• sterkt = strong

This is very similar to English:

• The steel is strong.

It can describe both.

Norwegian sterk can be used for:

• a strong person
• strong coffee
• a strong engine
• strong material
• strong steel

So in Stålet er sterkt, it naturally describes the physical strength of the steel.

Yes, it is important. Å is a separate letter in Norwegian, not just an a with a mark.

So:

• stål and stal are not the same thing
• å comes near the end of the Norwegian alphabet

You should treat å as its own vowel.

A simple learner-friendly approximation is:

• STO-let er sterkt

A few helpful points:

• stål has a long vowel, something like stoal/stohl
• stålet is roughly STO-leh(t)
• sterkt ends with a consonant cluster, so it may feel a little heavy to pronounce

You do not need perfect pronunciation immediately; the key thing is to notice:

• å in stål
• the extra syllable in stålet
• the -t ending in sterkt

Very often, yes, in the singular.

Typical pattern:

• en sterk bil = a strong car
• et sterkt materiale = a strong material

But there are a few things to remember:

1. This is mainly about singular neuter.
2. In the plural or with definite noun phrases, adjectives often take -e instead:
   • sterke materialer = strong materials
   • det sterke stålet = the strong steel
3. Some adjectives are irregular, but sterk → sterkt is a regular pattern.

It could be, but that would mean something slightly different.

• Stålet er sterkt. = The steel is strong.
• Det stålet er sterkt. = That steel is strong / That particular steel is strong

Adding det points to a specific one more explicitly.

So the shorter sentence is completely normal when you just mean the steel.

No. Norwegian does not capitalize all nouns.

So you write:

• stålet er sterkt

But since this is the beginning of a sentence, it becomes:

• Stålet er sterkt.

Only the first word of the sentence is capitalized here, not the noun because it is a noun.

Yes. This is the basic and very common word order:

• Subject + verb + adjective/complement

So:

• Stålet = subject
• er = verb
• sterkt = complement

This is the same basic pattern as English:

• The steel is strong.