Vi slår teltet op på campingpladsen ved søen.

Because slå op is a phrasal / multi-word verb in Danish. In this sentence, slår is the finite verb, and op is the particle.

In a normal main clause, Danish often places the particle later in the sentence:

• Vi slår teltet op = We put the tent up / set the tent up

This is similar to English set up, which can also be split:

• We set the tent up
• We set up the tent

In Danish, this split is very common in main clauses.

Yes, slå often means hit, strike, or beat, but in combinations with particles, it can take other meanings.

Here, slå teltet op is a fixed expression meaning:

• put up a tent
• pitch a tent
• set up a tent

So you should learn slå op here as part of the camping expression slå et telt op.

A few examples:

• Vi slår teltet op nu. = We’re putting the tent up now.
• De slog teltene op ved stranden. = They pitched the tents by the beach.

Teltet means the tent, while et telt means a tent.

The ending -et is the definite article attached to a neuter noun:

• et telt = a tent
• teltet = the tent

So in Danish, instead of using a separate word for the, you often add it to the end of the noun.

This sentence is talking about the tent, not just any tent.

For the same reason as teltet: Danish usually expresses the by adding a definite ending to the noun.

• en campingplads = a campsite / campground

• campingpladsen = the campsite / the campground

• en sø = a lake
• søen = the lake

For common gender nouns, the definite ending is often -en.
For neuter nouns, it is often -et.

So:

• teltet = the tent
• campingpladsen = the campsite
• søen = the lake

Because Danish uses på with certain locations where English might use at, on, or sometimes in.

Here:

• på campingpladsen = at the campsite / on the campsite grounds

This is idiomatic Danish. You should learn it as the normal preposition with campingplads in this kind of context.

Other common examples:

• på skolen = at the school
• på kontoret = at the office
• på landet = in the countryside

So even if English would not literally say on the campsite, Danish naturally says på campingpladsen.

Ved usually means by, near, or next to.

So:

• ved søen = by the lake / near the lake

It tells you the location of the campsite more precisely: the campsite is by the lake.

Compare:

• på campingpladsen = at the campsite
• ved søen = by the lake

Together:

• på campingpladsen ved søen = at the campsite by the lake

Yes, it is completely normal.

The structure is:

• Vi = subject
• slår = finite verb
• teltet = object
• op = particle
• på campingpladsen = place
• ved søen = extra location detail

So the sentence follows ordinary Danish main-clause word order.

A very literal breakdown would be:

• We put the tent up at the campsite by the lake.

No, that would not sound right in standard Danish.

With this kind of verb-particle structure in a main clause, the normal pattern is:

• Vi slår teltet op

not:

• Vi slår op teltet

So the object teltet normally comes before the particle op here.

Slår is present tense.

The infinitive is:

• at slå = to strike / to hit / to put up (in this expression)

Present tense:

• jeg slår
• du slår
• vi slår

Danish verbs do not change form for different persons in the present tense, so slår stays the same with I, you, we, they, etc.

Depending on context, the present tense can also be used for near-future meaning, just like in English:

• Vi slår teltet op i morgen. = We’re putting up the tent tomorrow.

Because Danish verbs are much simpler than English in this respect. The verb usually has one present-tense form for all persons.

For example, with at slå:

• jeg slår = I hit / I put up
• du slår = you hit / you put up
• vi slår = we hit / we put up
• de slår = they hit / they put up

So vi simply means we, and the verb does not need a special we ending.

In practice, it can support the whole situation, but most naturally ved søen is understood as describing campingpladsen:

• på campingpladsen ved søen = at the campsite by the lake

So the listener will usually understand that it is the campsite that is located by the lake.

If you wanted to emphasize the tent being set up by the lake itself, Danish would usually make that clearer in another way.

It can mean either, depending on the variety of English you use.

• In British English, campsite is often a good translation.
• In American English, campground may sound more natural.

So:

• på campingpladsen = at the campsite / at the campground

Both are fine.

The past tense of slår here is slog.

So:

• Vi slog teltet op på campingpladsen ved søen.
• We put the tent up / pitched the tent at the campsite by the lake.

That is a very useful pattern to remember:

• slår = present
• slog = past
• har slået = have put up / have struck

In this camping expression:

• Vi har slået teltet op. = We have put the tent up.

Yes, very natural.

Slå et telt op is one of the standard Danish expressions for put up / pitch a tent. If you want to sound natural when talking about camping, this is exactly the kind of phrase to learn as a chunk.

Useful related examples:

• Skal vi slå teltet op her? = Shall we put the tent up here?
• De slog telt op i skoven. = They pitched a tent in the forest.
• Hvor kan man slå telt op? = Where can you pitch a tent?