Hvis pletten ikke går af, bruger jeg stoffet som klud i stedet for at beholde skjorten.

Here gå af means come off, come out, or wash out.

So pletten ikke går af means the stain does not come out of the fabric.

This is a common Danish particle verb:

• Pletten går af. = The stain comes out.
• Det går ikke af. = It does not come off.

The meaning is idiomatic here, not a literal walk off.

Because this is a subordinate clause introduced by hvis.

In Danish, subordinate clauses usually put sentence adverbs like ikke before the finite verb:

• Hvis pletten ikke går af ...

Compare that with a main clause:

• Pletten går ikke af.

So the pattern is:

• Main clause: subject + verb + ikke
• Subordinate clause: subject + ikke
  • verb

That is one of the most important word-order differences in Danish.

Because Danish main clauses follow the V2 rule: the finite verb must be in the second position.

The whole Hvis pletten ikke går af clause takes the first position, so the next main clause begins with the verb:

• Hvis pletten ikke går af, bruger jeg stoffet ...

If you started directly with the main clause, you would say:

• Jeg bruger stoffet som klud ...

So the inversion happens because something else comes first.

Stof usually means fabric, material, or cloth.

So stoffet literally means the fabric/material. In this sentence, it refers to the shirt as fabric — basically, if the stain will not come out, I will treat the shirt as just cloth and use it as a rag.

That sounds a bit blunt in Danish too. It reduces the shirt from a wearable item to mere material.

Using stoffet shifts the focus from the shirt as clothing to the shirt as material.

That makes the idea very clear:

• If the stain stays, the shirt is no longer worth keeping as a shirt.
• It will just become fabric for cleaning.

So this is not random variation; it helps express the speaker’s attitude.

After som, Danish often uses a noun without an article when describing a role, function, or use.

So:

• bruge noget som klud = use something as a rag
• arbejde som lærer = work as a teacher

The bare noun sounds natural because it describes function, not identity.

You could sometimes hear an article in other contexts, but here som klud is the normal and natural phrasing.

I stedet for means instead of.

When it is followed by a verb, Danish normally uses at + infinitive:

• i stedet for at beholde skjorten = instead of keeping the shirt

So the structure is:

• i stedet for + noun
• i stedet for at + infinitive

Examples:

• i stedet for kaffe = instead of coffee
• i stedet for at vente = instead of waiting

Beholde means keep, retain, or not get rid of.

So:

• beholde skjorten = keep the shirt

Holde is a different verb with meanings like hold, keep, last, or have depending on context, but it is not the normal verb for keep an object and continue owning it in this situation.

So:

• Jeg beholder skjorten. = I’m keeping the shirt.

That is the natural choice here.

Because the sentence is talking about specific things:

• pletten = the stain
• stoffet = the fabric
• skjorten = the shirt

Danish often uses the suffixed definite article:

• en plet → pletten
• et stof → stoffet
• en skjorte → skjorten

The sentence assumes the speaker and listener know which stain and which shirt are meant.

Danish often uses the present tense for future meaning, especially when the context already makes the time clear.

So:

• Hvis pletten ikke går af, bruger jeg stoffet som klud ...

means something like:

• If the stain doesn’t come out, I’ll use the fabric as a rag ...

English often uses will, but Danish frequently just uses the present tense in this kind of conditional sentence.

In a sentence like this, yes.

Hvis is the normal word for if in conditional statements:

• Hvis det regner, bliver jeg hjemme. = If it rains, I’m staying home.

So here:

• Hvis pletten ikke går af ... = If the stain doesn’t come out ...

It introduces the condition for what happens next.

It is a verb + particle combination, and you should learn it as one unit: gå af.

In this sentence:

• går is the finite verb
• af is the particle

Together they create the meaning come off / come out.

This matters because the meaning is not always predictable from gå alone. If you only think of gå as walk/go, the sentence will be confusing. Danish has many such combinations, and they are best learned as fixed expressions.

Yes, Danish has other possible ways to express the idea, such as:

• Hvis pletten ikke kan komme af
• Hvis pletten ikke kan vaskes af
• Hvis jeg ikke kan få pletten af

But the sentence you were given, Hvis pletten ikke går af, is very natural and concise.

The difference is mainly in perspective:

• pletten går af = the stain comes off
• jeg får pletten af = I get the stain off
• pletten kan vaskes af = the stain can be washed off

All are useful, but the original sentence is perfectly idiomatic.