Sig til, hvis du har brug for hjælp.

Sig is the imperative form of at sige (to say / to tell).

So Sig til means say so / let me know / tell me.

In Danish, the imperative is often just the verb stem:

• at sige → sig
• at komme → kom
• at vente → vent

So the sentence begins with a direct instruction: Let me know ...

Sig til is a very common expression in Danish. It does not literally mean just say to in the English sense. As a phrase, it usually means:

• let someone know
• speak up
• tell someone
• say if something is needed

In this sentence, Sig til is best understood as Let me know.

You can also hear it in other situations:

• Sig til, når du er klar. = Let me know when you’re ready.
• Sig til, hvis der er noget galt. = Let me know if something is wrong.

In Danish imperatives, the subject you is usually not stated, just like in English.

Compare:

• English: Come here.
• Danish: Kom her.

The you is understood automatically.

So Sig til already means You, tell me / let me know without needing du.

Hvis means if.

It introduces a condition:

• hvis du har brug for hjælp = if you need help

So the full sentence means something like:

• Let me know if you need help.

A learner should notice that hvis introduces a subordinate clause.

Because after hvis, Danish normally uses subordinate-clause word order, which is usually:

• subject + verb

So:

• hvis du har brug for hjælp

not

• hvis har du brug for hjælp

This is similar to English, where we also say:

• if you need help

not

• if need you help

At have brug for is a fixed expression meaning to need.

Literally, it is closer to to have use for, but in real Danish it simply means to need.

Examples:

• Jeg har brug for vand. = I need water.
• Har du brug for hjælp? = Do you need help?

So in your sentence:

• du har brug for hjælp = you need help

This is a very useful expression and worth learning as a chunk.

Here hjælp means help in a general, uncountable sense, just like in English.

Compare:

• I need help.
• Jeg har brug for hjælp.

No article is needed when you mean help in general.

If you used en hjælp, that would usually mean a help / a helpful thing or person, which is a different idea and much less natural here.

The comma separates the main clause from the subordinate clause introduced by hvis.

• Main clause: Sig til
• Subordinate clause: hvis du har brug for hjælp

So the comma helps show the structure clearly.

In standard written Danish, this comma is normal and expected.

It is usually perfectly polite and very common.

Even though it uses the imperative, it often functions as a friendly invitation:

• Let me know if you need help.

It does not usually sound harsh.

If you want to make it sound even softer or warmer, Danish often adds words like:

• Du må sige til, hvis du har brug for hjælp.
• Sig endelig til, hvis du har brug for hjælp.

These feel a bit more like:

• Please do let me know if you need help.

Yes. Sig til! can stand alone.

Depending on context, it can mean things like:

• Let me know!
• Tell me!
• Speak up!

The exact meaning depends on the situation.

For example:

• Hvis du bliver træt, så sig til. = If you get tired, let me know.
• Sig til, når vi skal gå. = Tell me when we should leave.

Hjælp can be tricky for English speakers.

A rough guide:

• the hj combination is not pronounced like clear English hy
• the vowel sound is somewhat like a short open e/æ sound
• the word ends with lp, where the p may be quite light

A very rough approximation might be something like hyelp or yelp, but neither is exact.

The biggest thing to remember is that Danish pronunciation is often less direct than spelling suggests, so it is best to hear this word from native audio and repeat it several times in whole phrases like:

• brug for hjælp
• har du brug for hjælp?

Usually, no.

In this sentence, hvis is the normal word for if in a conditional sense:

• if you need help

Om can sometimes mean whether / if, but that is a different kind of if.

Compare:

• Sig til, hvis du har brug for hjælp. = Let me know if you need help.
• Jeg ved ikke, om du har brug for hjælp. = I don’t know whether you need help.

So here, hvis is the correct choice.