Fjarlægðu blettinn af skyrtunni.

Fjarlægðu is the singular informal imperative of fjarlægja (to remove). It is the form you use when giving a command to one person, like Remove ...

So:

• fjarlægja = to remove
• fjarlægðu! = remove!

Icelandic often leaves out the subject in commands, just like English does:

• Fjarlægðu blettinn = Remove the stain

If you were speaking to more than one person, or using the plural command form, you would use fjarlægið instead.

In Icelandic, commands usually do not need an explicit subject pronoun. The verb form itself already tells you that it is a command.

So:

• Fjarlægðu blettinn af skyrtunni. = Remove the stain from the shirt.

This works much like English Sit down!, Open the door!, where you is understood.

Because blettinn is the accusative singular definite form of blettur (stain, spot).

Here is the breakdown:

• blettur = a stain / stain (nominative singular)
• blett = stain (accusative singular, indefinite)
• blettinn = the stain (accusative singular, definite)

The verb fjarlægja takes a direct object, and that object is in the accusative case. Since the sentence means the stain, Icelandic uses the definite ending too.

So:

• Fjarlægðu blett = Remove a stain
• Fjarlægðu blettinn = Remove the stain

Because af normally takes the dative case, and skyrtunni is the dative singular definite form of skyrta (shirt).

Here is the pattern:

• skyrta = shirt
• skyrtan = the shirt (nominative singular)
• skyrtu = shirt (accusative/dative singular indefinite, depending on context)
• skyrtunni = the shirt (dative singular definite)

Since the phrase is af skyrtunni (from the shirt / off the shirt), the noun after af must be in the dative.

Here af means from or off.

So:

• af skyrtunni = from the shirt / off the shirt

In this sentence, English could naturally say either:

• Remove the stain from the shirt
• Remove the stain off the shirt

The first is more standard English, but both help show what af is doing: it marks the thing something is being removed from.

This is a very useful sentence for seeing Icelandic case grammar in action:

• Fjarlægðu — imperative verb
• blettinn — accusative singular definite, because it is the direct object
• af skyrtunni — dative singular definite after the preposition af

So the structure is:

• Verb + object in accusative + af + noun in dative

That is one of the most important things to notice here.

Icelandic usually expresses the as a suffix attached to the noun, rather than as a separate word like English the.

So:

• blettinn = the stain
• skyrtunni = the shirt

This is very normal in Icelandic. English says:

• the stain
• the shirt

But Icelandic often builds the definiteness right into the noun ending.

Yes, but it would not mean exactly the same thing in tone or style.

• Fjarlægðu means remove
• Taktu ... af literally means take ... off/from

In many situations, both could be understood, but fjarlægja sounds a bit more direct and standard for removing something, especially in instructions or formal contexts.

So:

• Fjarlægðu blettinn af skyrtunni = more neutral/instructional
• Taktu blettinn af skyrtunni = more literal, and less natural depending on context

For a stain specifically, Icelandic might also use other verbs depending on context, but fjarlægðu is perfectly good.

You would usually use the plural imperative:

• Fjarlægið blettinn af skyrtunni.

So:

• fjarlægðu = command to one person
• fjarlægið = command to more than one person

This is a very common distinction in Icelandic.

A rough learner-friendly pronunciation is:

• FJAR-lai-ghthoo or FYAR-lai-ghthoo

A few helpful notes:

• fj at the start often sounds a bit like fy
• æ sounds like the i in fine for many learners' ears
• ð in -ðu is like the th in this
• the final u is a short vowel, roughly like German u or a rounded vowel that English does not match perfectly

You do not need perfect pronunciation right away, but the important part is recognizing that -ðu is the imperative ending here.

The normal and most natural order here is:

• Fjarlægðu blettinn af skyrtunni.

That is:

• verb
• direct object
• prepositional phrase

Because Icelandic has case endings, word order can sometimes move around more than in English, especially for emphasis. But for a straightforward command, the version you have is the most natural one to learn first.

The dictionary forms are:

• fjarlægja = to remove
• blettur = stain, spot
• af = from, off
• skyrta = shirt

The sentence uses inflected forms of those words:

• Fjarlægðu ← from fjarlægja
• blettinn ← from blettur
• skyrtunni ← from skyrta

This is very typical in Icelandic: the forms you see in real sentences are often different from the dictionary form because of case, number, definiteness, or verb form.