Musikkfrasen følger taktarten.

Because -en marks the definite singular form of the noun.

• en musikkfrase = a musical phrase
• musikkfrasen = the musical phrase

In Norwegian, definiteness is often added as a suffix to the noun instead of using a separate word like the.

For the same reason: it is also in the definite singular form.

• en taktart = a time signature / a meter
• taktarten = the time signature / the meter

So both nouns in the sentence are definite:

• musikkfrasen = the musical phrase
• taktarten = the time signature

Because Norwegian usually expresses definiteness by attaching it to the noun itself.

So instead of saying something like the musical phrase, Norwegian often says:

• musikkfrasen

and instead of the time signature:

• taktarten

A separate determiner like den is usually used when there is an adjective:

• den musikalske frasen = the musical phrase

But in your sentence, there is no adjective, so the suffix alone is enough.

Følger is the present tense of the verb å følge.

• å følge = to follow
• følger = follows / is following

Norwegian verbs do not change for person:

• jeg følger = I follow
• du følger = you follow
• han følger = he follows
• de følger = they follow

So følger works for all subjects in the present tense.

Because følge is the infinitive form, like to follow in English.

After a subject in a normal statement, you need a finite verb, and here that is the present tense:

• Musikkfrasen følger taktarten.

If you used the infinitive, it would be ungrammatical in this sentence.

You would use følge after å:

• å følge taktarten = to follow the time signature

It follows the normal Norwegian main-clause pattern:

Subject + Verb + Object

• Musikkfrasen = subject
• følger = verb
• taktarten = object

So it is very similar to English:

• The musical phrase follows the time signature.

Yes. Norwegian very often combines words into one compound noun.

• musikk = music
• frase = phrase
• musikkfrase = musical phrase / music phrase

This is completely normal in Norwegian. English often writes similar ideas as two words, but Norwegian commonly makes them one word.

Taktart usually means time signature or meter, depending on context.

It is built from:

• takt = beat / bar / measure
• art = kind / type

So literally it is something like type of meter/beat structure. In music contexts, time signature is often the most natural English equivalent.

Yes, depending on context.

Norwegian simple present often covers both:

• follows
• is following

So Musikkfrasen følger taktarten can describe:

• a general fact, or
• something happening right now

Context tells you which meaning is intended.

A rough guide is FURL-ger, but that is only approximate.

The hardest part for English speakers is ø, which does not have an exact English equivalent. It is a rounded front vowel. A useful tip is:

• say something like eh or uh
• while rounding your lips

Also note:

• g in følger is pronounced
• the word has two syllables: føl-ger

A rough learner-friendly pronunciation might be written as:

• FUHL-ger or FURL-ger

but neither is perfect.

This is because of how the nouns are formed in the definite singular.

For many common-gender nouns ending in -e, the definite singular often adds just -n:

• en frase → frasen

For many common-gender nouns ending in a consonant, the definite singular adds -en:

• en taktart → taktarten

So:

• musikkfrase → musikkfrasen
• taktart → taktarten

Not normally, unless you mean something more like that musical phrase.

• musikkfrasen = the musical phrase
• den musikkfrasen = that musical phrase

So adding den changes the meaning. In your sentence, plain musikkfrasen is the normal way to say the musical phrase.

Yes. Because both nouns are definite singular, the sentence refers to specific, identifiable things:

• musikkfrasen = the specific musical phrase
• taktarten = the specific time signature

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

• En musikkfrase følger en taktart.

But that sounds more abstract and less natural in many contexts. Your original sentence points to particular items already understood from the context.