Navet lager en lyd.

Because navet is the definite singular form.

• et nav = a hub
• navet = the hub

The noun nav is neuter, so its definite ending is -et.
English uses a separate word, the, but Norwegian often puts definiteness at the end of the noun instead.

It is singular.

Here is the pattern:

• et nav = a hub
• navet = the hub
• nav / naver or other plural forms depending on usage/context = plural forms

So in this sentence, we are talking about one hub, not several.

Because lyd takes the article en in Bokmål.

• en lyd = a sound
• lyden = the sound

Norwegian nouns have grammatical gender, and the article depends on the noun:

• en for many masculine/common-gender nouns
• et for neuter nouns
• ei for feminine nouns in forms that use it

So lyd goes with en, not et.

Here, lager is the present tense of lage, which often means make.

So lager en lyd literally means makes a sound.

In natural English, that may also be understood as:

• makes a noise
• is making a sound
• produces a sound

So lager here has the sense of produces.

Because Norwegian usually uses the simple present where English might use either:

• makes
• is making

So Navet lager en lyd can mean:

• The hub makes a sound
• The hub is making a sound

The exact meaning depends on context. Norwegian does have ways to stress ongoing action, but in an ordinary sentence like this, the simple present is the normal choice.

The word order is the basic subject–verb–object pattern:

• Navet = subject
• lager = verb
• en lyd = object

So the structure is:

Navet + lager + en lyd
The hub + makes + a sound

This is the most straightforward main-clause order in Norwegian.

Yes, you can, but the meaning is slightly different.

• Navet lager en lyd = The hub makes a sound
  This can suggest a particular sound or a sound event.

• Navet lager lyd = The hub makes noise / is noisy
  This is more general.

So both are possible, but en lyd is a bit more specific than just lyd.

The tricky part is the vowel y.

In Norwegian, y is pronounced with rounded lips. It is similar to:

• French u
• German ü

It is not pronounced like English y in yes.

A rough guide:

• lyd sounds approximately like lüüd, but that is only an approximation
• the d at the end is pronounced

For many English speakers, the best tip is:

1. Say ee
2. Keep that tongue position
3. Round your lips

That gets you closer to the Norwegian y sound.