Om aftenen går ræven forbi teltet.

This is because Danish main clauses normally follow the V2 rule: the finite verb must be in the second position.

Here, Om aftenen is placed first as a time expression, so the verb går has to come next:

• Om aftenen = first position
• går = second position
• ræven = subject, after the verb

So:

• Om aftenen går ræven forbi teltet.

If you start with the subject instead, you get:

• Ræven går forbi teltet om aftenen.

Both are grammatical, but the first one emphasizes the time.

Om aftenen usually means in the evening or in the evenings. It often has a general or habitual feeling.

So this sentence may suggest something like:

• In the evening, the fox passes by the tent
• or In the evenings, the fox goes past the tent

By contrast, i aften means this evening / tonight and refers to a specific evening.

Compare:

• Om aftenen går ræven forbi teltet. = in the evening / in the evenings
• I aften går ræven forbi teltet. = the fox will pass by the tent this evening

Also note: i aftenen is generally not what you want here.

In this expression, Danish normally uses the definite form:

• om morgenen = in the morning
• om aftenen = in the evening
• om natten = at night / during the night

So om aftenen is a common fixed time expression. Even though English says in the evening without attaching the article to the noun, Danish does it with the definite ending:

• aften = evening
• aftenen = the evening

Because Danish nouns belong to different grammatical genders, and the definite article is usually added to the end of the noun.

• en ræv = a fox

• ræven = the fox

• et telt = a tent
• teltet = the tent

So:

• -en is the usual definite ending for common gender nouns
• -et is the usual definite ending for neuter nouns

That is why you get ræven but teltet.

In this sentence, forbi is best understood as part of the expression gå forbi, which means go past or pass by.

So:

• gå forbi = to pass by / to go past

In the sentence:

• går ræven forbi teltet

the meaning is that the fox goes past the tent.

You can think of forbi as a directional word that works closely with the verb. Danish often has these verb + particle combinations.

It can mean both, depending on context.

The basic meaning of gå is walk or go on foot, but with animals it is also natural to use it for moving along on foot. In this sentence, går forbi is very naturally understood as:

• walks past
• goes past
• passes by

So you should not read it too narrowly as only walks in a very literal English sense.

It often sounds habitual or general, especially because of om aftenen.

So many learners would hear this as something like:

• In the evenings, the fox passes by the tent
• The fox goes past the tent in the evening

If you wanted a clearly one-time event in the past, Danish would more likely use a more specific time expression, for example:

• I aftes gik ræven forbi teltet. = Last night / yesterday evening, the fox went past the tent.

If you wanted a specific future/present evening:

• I aften går ræven forbi teltet. = This evening, the fox will go past the tent.

Yes. That is also correct.

Compare:

• Om aftenen går ræven forbi teltet.
• Ræven går forbi teltet om aftenen.

The difference is mostly focus:

• starting with Om aftenen puts more emphasis on when
• starting with Ræven is a more neutral subject-first sentence

Both are natural Danish.

Because Danish usually expresses definiteness by adding it to the end of the noun, instead of using a separate article like English the.

So:

• en ræv = a fox

• ræven = the fox

• et telt = a tent
• teltet = the tent

English uses a separate word (the fox, the tent), but Danish usually uses a suffix.

Yes, in practical learner terms, teltet is what the fox passes by, so it functions like the object/complement after forbi.

Structure:

• Om aftenen = time expression
• går = finite verb
• ræven = subject
• forbi teltet = the “past the tent” part

So the core idea is:

• The fox goes/passes by the tent in the evening.

Even if Danish structures this slightly differently from English, teltet is the thing being passed.