Noteheftet og øvingsfilen hjelper tenoren med repertoaret.

Those endings mark the definite singular form, roughly equivalent to English the.

In this sentence:

• noteheftet = the music booklet / score booklet
• øvingsfilen = the practice file
• tenoren = the tenor
• repertoaret = the repertoire

The ending depends on the noun’s grammatical gender:

• en tenor → tenoren
• en fil → filen
• et notehefte → noteheftet
• et repertoar → repertoaret

So -en is common with masculine/common-gender nouns, while -et is common with neuter nouns.

In Norwegian, the is usually attached to the end of the noun instead of standing as a separate word.

So instead of:

• the tenor
• the repertoire

Norwegian often uses:

• tenoren
• repertoaret

This is one of the biggest differences from English. In a simple noun phrase with no adjective, the ending alone is enough.

Yes. Norwegian uses compound nouns very freely.

• notehefte = note
  • hefte
• øvingsfil = øving
  • fil

Then the definite ending is added:

• notehefte → noteheftet
• øvingsfil → øvingsfilen

This is extremely common in Norwegian, so learners should get used to seeing long nouns built from smaller parts.

The -s- is a linking element used in many Norwegian compound nouns.

So:

• øving = practice, rehearsal
• fil = file
• øvingsfil = practice file

That s does not have a separate meaning like possession here. It just helps connect the two parts of the compound. English learners often want to translate it literally, but it is usually best to think of it as a normal part of compound formation.

Because Norwegian verbs do not change depending on whether the subject is singular or plural.

So:

• jeg hjelper
• du hjelper
• han hjelper
• vi hjelper
• de hjelper

The same present-tense form is used for all persons and numbers.

That means Noteheftet og øvingsfilen hjelper ... is completely normal, even though the subject has two items.

Hjelper is the present tense of å hjelpe (to help).

• å hjelpe = infinitive
• hjelper = present tense

So the sentence means that the booklet and the practice file help the tenor.

Because Norwegian often uses the pattern:

hjelpe noen med noe
= help someone with something

So here:

• hjelper tenoren = helps the tenor
• med repertoaret = with the repertoire

This is a very common construction. If you learn hjelpe noen med noe as a set pattern, sentences like this become much easier to understand and build yourself.

In a normal Norwegian main clause, the subject usually comes before the finite verb, and the object comes after it.

Here:

• Noteheftet og øvingsfilen = subject
• hjelper = verb
• tenoren = object

So the sentence means:

The music booklet and the practice file help the tenor ...

not

The tenor helps the music booklet and the practice file ...

Word order is doing most of the work here.

The sentence follows the normal Norwegian main-clause pattern:

Subject + verb + object + prepositional phrase

So:

• Noteheftet og øvingsfilen = subject
• hjelper = verb
• tenoren = object
• med repertoaret = prepositional phrase

This is a very standard, learner-friendly sentence pattern in Norwegian.