Ef þú misskilur mig aftur, skal ég útskýra þetta nánar.

Ef means if and introduces a conditional clause.

So Ef þú misskilur mig aftur = If you misunderstand me again.

In Icelandic, it is very common to put the if-clause first, just like in English.

Misskilur means misunderstand(s).

It comes from the verb að misskilja = to misunderstand.

You can think of it as:

• mis- / miss- = wrong, wrongly
• skilja = understand

So misskilja is literally something like understand wrongly.

In the sentence, misskilur is the present tense form used with þú:

• þú misskilur = you misunderstand

Because þú means you (singular, informal), and Icelandic verbs change depending on the subject.

Here:

• ég misskil = I misunderstand
• þú misskilur = you misunderstand
• hann/hún/það misskilur = he/she/it misunderstands

So misskilur is the correct present-tense form for þú.

Because mig is the accusative form of ég.

The verb að misskilja takes a direct object, so the person being misunderstood appears in the accusative:

• ég = I
• mig = me

So:

• þú misskilur mig = you misunderstand me

This is similar to English I / me.

Aftur means again.

So:

• þú misskilur mig aftur = you misunderstand me again

It usually comes after the object in this sentence, though Icelandic word order can sometimes vary for emphasis.

The comma separates the conditional clause from the main clause:

• Ef þú misskilur mig aftur, = if you misunderstand me again
• skal ég útskýra þetta nánar. = I will explain this more clearly/in more detail.

This is very similar to English punctuation when an if-clause comes first.

Skal is the 1st person singular form of skulu.

In modern Icelandic, skulu can express something like:

• shall
• will
• sometimes am going to
• sometimes a sense of intention, determination, or promise

So skal ég útskýra þetta nánar means something like:

• I shall explain this in more detail
• I will explain this more clearly
• I’ll explain this further

In this sentence, it sounds a bit firmer or more deliberate than a plain future idea.

This is because Icelandic follows the verb-second rule in main clauses.

The sentence starts with a subordinate clause:

• Ef þú misskilur mig aftur

After that, the main clause begins, and the finite verb comes first:

• skal ég útskýra þetta nánar

So although the normal simple order is often:

• Ég skal útskýra þetta nánar

after a fronted clause it becomes:

• Ef ..., skal ég ...

This is a very important Icelandic word-order pattern.

Útskýra is the infinitive verb meaning to explain.

The dictionary form is að útskýra = to explain.

In the sentence:

• skal ég útskýra = I shall/will explain

So skal is the finite verb, and útskýra stays in the infinitive.

Þetta means this.

Here it refers to this matter / this thing / this point.

It is the neuter form, and it works as the object of útskýra:

• útskýra þetta = explain this

Learners often notice forms like:

• þessi = this
• þetta = this (neuter / often used pronominally)

In this sentence, þetta is best understood simply as this.

Nánar means more closely, more specifically, in more detail, or more clearly, depending on context.

It is the comparative adverb related to nær / nánari / nákvæmari-type detail meanings, and in this sentence it means:

• in more detail
• more fully

So:

• útskýra þetta nánar = explain this in more detail

This is a very common Icelandic expression.

It is not wrong or unnatural, but skal can sound a bit more formal, firm, or deliberate than the most neutral everyday future phrasing.

Depending on context, Icelanders might also say things like:

• þá útskýri ég þetta nánar
• ég skal útskýra þetta nánar
• ég get útskýrt þetta nánar

But the sentence you have is perfectly good Icelandic and has a slightly firm tone: If you misunderstand me again, I will explain it more clearly/in more detail.

Þú is singular informal you, used when speaking to one person.

If you were addressing more than one person, Icelandic would use þið instead.

So this sentence is directed at one person:

• Ef þú misskilur mig aftur ...

Grammatically, you could match some words that way, but that would sound wrong or misleading in natural English.

A better translation is:

• If you misunderstand me again, I will explain this in more detail.
• If you misunderstand me again, I’ll explain this more clearly.

The important point is that skal ég here is not really asking a question; it is a statement with Icelandic main-clause word order after the fronted if-clause.