Hvis min ven kommer på besøg i aften, laver jeg kaffe.

Because Danish main clauses normally follow the V2 rule: the finite verb goes in second position.

In this sentence, the whole Hvis ... i aften clause comes first:

• Hvis min ven kommer på besøg i aften, ...

That entire clause counts as the first element. So in the main clause, the verb must come next:

• laver jeg kaffe

This is the same pattern you see in many Danish sentences when something other than the subject comes first:

• I dag laver jeg kaffe.
• Hvis det regner, bliver vi hjemme.

If the main clause came first, you would get normal subject-verb order:

• Jeg laver kaffe, hvis min ven kommer på besøg i aften.

Danish often uses the present tense to talk about the future, especially when the future time is already clear from context.

Here, i aften tells you it is about the future, so kommer is completely natural:

• Hvis min ven kommer på besøg i aften ...

This works much like English in sentences such as:

• If my friend comes over tonight, I’ll make coffee.

English also often uses present tense in if-clauses, so this part is actually quite similar.

På besøg is a very common expression meaning visiting / on a visit / over for a visit.

So:

• kommer på besøg = comes to visit / comes over

It is best learned as a set expression.

Examples:

• Vi er på besøg hos mine forældre. = We are visiting my parents.
• Han kommer på besøg i morgen. = He is coming over tomorrow.

You usually would not translate it word-for-word. It functions as an idiomatic phrase.

Use hvis when something is conditional: it may happen, but it may also not happen.

• Hvis min ven kommer på besøg i aften ... = If my friend comes over tonight ...

Use når when something is seen as expected or certain to happen at some point:

• Når min ven kommer på besøg, laver jeg altid kaffe. = When my friend comes to visit, I always make coffee.

So in your sentence, hvis suggests: maybe the friend will come, maybe not.

Yes, in standard Danish writing, a comma is normally used before the main clause here:

• Hvis min ven kommer på besøg i aften, laver jeg kaffe.

The first part is a subordinate clause introduced by hvis, and the second part is the main clause.

Danish comma rules have had some variation over time, but in normal modern writing, this comma is expected and helpful.

In Danish, lave is often used where English uses make.

So:

• lave kaffe = make coffee

Gøre is not the normal verb here. Gøre often means do, make in the sense of cause/make someone do something, or appears in fixed expressions.

For coffee, Danish commonly says:

• lave kaffe = make coffee
• brygge kaffe = brew coffee

Brygge kaffe sounds a bit more specifically about the brewing process, while lave kaffe is the everyday general choice.

Because kaffe here is being used as an uncountable/mass noun, like coffee in English.

So Danish says:

• Jeg laver kaffe. not
• Jeg laver en kaffe.

En kaffe usually means a coffee as a serving/order, for example in a café:

• Jeg vil gerne have en kaffe.

But when you mean the drink in general, Danish normally uses just kaffe with no article.

Traditionally, yes:

• ven = male friend
• veninde = female friend

So min ven usually means my male friend.

That said, real-life usage can be a bit broader in some contexts, and people do not always focus strongly on the gender distinction. But for learners, the safest rule is:

• min ven = my male friend
• min veninde = my female friend

I aften is the normal fixed expression for tonight / this evening.

Time expressions in Danish often have their own idiomatic form, so they are not always built the way an English speaker might expect.

Common examples:

• i dag = today
• i morgen = tomorrow
• i aften = tonight / this evening
• i nat = tonight (during the night)

I aftenen is generally not the normal way to say tonight.

Yes, absolutely.

That version is also correct:

• Jeg laver kaffe, hvis min ven kommer på besøg i aften.

The difference is mainly one of focus and word order:

• Hvis min ven kommer på besøg i aften, laver jeg kaffe.

  • starts with the condition
  • gives a slightly more structured if X, then Y feel

• Jeg laver kaffe, hvis min ven kommer på besøg i aften.

  • starts with what you will do
  • sounds a bit more direct in everyday speech

Both are natural Danish.

Yes, you can, and it is perfectly natural:

• Hvis min ven kommer på besøg i aften, brygger jeg kaffe.

The difference is nuance:

• lave kaffe = make coffee
• brygge kaffe = brew coffee

Brygge is a little more specific and can sound slightly more connected to the actual preparation. Lave kaffe is broader and very common in everyday Danish.

Because Danish treats main clauses and subordinate clauses differently.

In the main clause, Danish follows the V2 rule:

• laver jeg kaffe

But in the subordinate clause, the normal order is more like:

• hvis min ven kommer på besøg i aften

So Danish is not simply inverting words everywhere. It keeps different patterns for different clause types:

• Main clause: verb in second position
• Subordinate clause: more regular subject-verb order

That is why the sentence combines:

• Hvis min ven kommer på besøg i aften
  with
• laver jeg kaffe