Festlokalet åpner nå.

Because Norwegian very often forms compound nouns by joining words together.

• fest = party / celebration
• lokale = venue / room / premises
• festlokale = party venue / function room
• festlokalet = the party venue / function room

This is much more common in Norwegian than in English, where we often write similar ideas as separate words.

The ending -et makes the noun definite singular for a neuter noun.

So:

• et festlokale = a party venue
• festlokalet = the party venue

Unlike English, Norwegian often puts the at the end of the noun instead of using a separate word.

You can tell from the article in the indefinite form:

• et festlokale = a party venue

The article et marks it as neuter.

That is why the definite singular becomes:

• festlokalet

Very roughly:

• masculine nouns often take -en
• feminine nouns often take -a
• neuter nouns often take -et

Åpner is the present tense of the verb å åpne = to open.

Examples:

• å åpne = to open
• åpner = opens / is opening
• åpnet = opened
• har åpnet = has opened

In Festlokalet åpner nå, åpner means opens or is opening, depending on context.

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

• opens
• is opening

So:

• Festlokalet åpner nå can mean The venue opens now or The venue is opening now

Norwegian does have ways to express ongoing action more explicitly, but in a basic sentence like this, the plain present tense is the normal choice.

Nå means now, and its placement here is very natural.

• Festlokalet åpner nå. = The venue is opening now.

Putting nå at the end keeps the sentence neutral and straightforward.
You can move it for emphasis:

• Nå åpner festlokalet. = Now the venue is opening.
• Festlokalet åpner nå. = The venue is opening now.

Both are possible, but they feel slightly different in emphasis.

Because Norwegian usually attaches definiteness to the noun itself.

So instead of:

• the venue

Norwegian often uses:

• lokalet
• festlokalet

The the idea is built into the ending.

This is one of the biggest differences from English noun structure.

Yes. Å åpne can be both transitive and intransitive.

• Jeg åpner døra. = I open the door.
  Here it has an object: døra.

• Døra åpner nå. = The door opens / is opening now.
  Here it has no object.

In your sentence:

• Festlokalet åpner nå.

the venue is treated as the thing that opens, which is perfectly natural.

Often yes, but the exact English word depends on context.

Festlokale can mean things like:

• function room
• event venue
• banquet hall
• party venue
• celebration venue

So festlokalet åpner nå could refer to anything from a rented hall to a special event space. The exact English wording depends on the situation.

Very literally, it is:

• Festlokalet = the party venue
• åpner = opens / is opening
• nå = now

So the structure is:

• The party venue opens now

But in natural English, depending on context, you might more often say:

• The venue is opening now.

That does not mean the Norwegian is unusual; it is just a normal difference between the two languages.