Husk at bruge blinklyset, før du drejer ind ved rundkørslen.

Because in Danish, at is normally used before an infinitive after verbs like huske when you mean remember to do something.

• Husk at bruge ... = Remember to use ...

This is very similar to English remember to use.

A few comparisons:

• Husk at ringe. = Remember to call.
• Husk at låse døren. = Remember to lock the door.

So at bruge is the infinitive structure here.

Husk is the imperative form of huske.

So:

• at huske = to remember
• husker = remember / remembers
• husk! = remember!

In this sentence, Husk is giving an instruction or reminder, just like English Remember.

Blinklyset is the definite singular form: the turn signal / the indicator.

The noun is:

• et blinklys = a turn signal / indicator
• blinklyset = the turn signal / the indicator

Danish often uses the definite form where English might sound more general. In a driving instruction, blinklyset refers to the signal on the vehicle as the relevant one you are supposed to use.

So bruge blinklyset is natural Danish for use the indicator/turn signal.

It has two useful parts:

• blinklys = turn signal / indicator
  
  • literally something like blinking light
• -et = the definite ending for many et-words

So:

• et blinklys
• blinklyset

This is a very common Danish pattern:

• et hus → huset
• et vindue → vinduet
• et blinklys → blinklyset

Because Danish often uses the present tense for future meaning, especially when the future is understood from the context.

So:

• før du drejer ind literally looks like before you turn in
• but it naturally means before you turn in / before you turn

English does this too in time clauses:

• Call me before you leave.
• not usually before you will leave

So Danish før du drejer ind works the same way.

Ind is a particle that adds the idea of in / into / inward.

• dreje = turn
• dreje ind = turn in / turn into

This is one of those verb + particle combinations that are very common in Danish.

Examples:

• dreje til venstre = turn left
• dreje ind = turn in / turn into
• gå ind = go in
• køre ind = drive in

So drejer ind is not just the physical act of turning the steering wheel; it suggests turning into a road or into the relevant route.

Ved usually means at, by, near and is often used for a location or reference point.

So:

• ved rundkørslen = at/by the roundabout

This tells you the turn is associated with that place.

By contrast:

• i rundkørslen = in the roundabout

That would mean physically inside the roundabout itself.

So ved rundkørslen is used because the roundabout is the point where the action happens or the place you are approaching.

Rundkørslen is the definite form:

• en rundkørsel = a roundabout
• rundkørslen = the roundabout

The sentence refers to a specific roundabout in the situation, so the definite form is natural.

This is very common in instructions when both speaker and listener know which thing is meant.

Not especially in this sentence. Før introduces a subordinate clause:

• før du drejer ind ved rundkørslen

The basic order here is:

• du = subject
• drejer = verb

So it looks straightforward: before you turn in at the roundabout.

A useful thing to know is that Danish subordinate clauses do not use the same kind of inversion you often see in main clauses.

Compare:

• Du drejer ind ved rundkørslen.
• ... før du drejer ind ved rundkørslen.

The subject stays before the verb.

Sometimes, yes, but blinklys is the common everyday Danish word for a vehicle’s turn signal/indicator.

Depending on region and context, learners may also hear:

• blinklys = turn signal / indicator
• viserblink or other variants are much less standard/common in everyday use

So for normal modern Danish, blinklyset is the safest and most natural word here.

A useful breakdown is:

• Husk = Remember
• at bruge blinklyset = to use the turn signal
• før = before
• du drejer ind = you turn in
• ved rundkørslen = at/by the roundabout

So the structure is basically:

Remember + to do something + before + clause

That makes it a very typical and useful Danish instruction pattern.