Þetta er það sem ég þarf að muna: eitt skref í einu.

Þetta means this, while það means that/it.

So Þetta er... is literally This is..., which matches the idea of introducing something specific:

• Þetta er það sem ég þarf að muna...
• This is what I need to remember...

If you used Það er, the meaning would shift more toward That is... or sometimes There is..., depending on context.

Það sem is a very common Icelandic structure meaning what in the sense of the thing that / that which.

So:

• það sem ég þarf að muna
• literally: that which I need to remember
• natural English: what I need to remember

This is one of the most useful patterns to learn in Icelandic.

Examples:

• Þetta er það sem ég vil. = This is what I want.
• Ég veit það sem þú sagðir. = I know what you said.

Sem is a relative particle, often translated as that, which, or sometimes left untranslated in natural English.

In það sem ég þarf að muna, it links það to the clause that explains it:

• það = that / the thing
• sem ég þarf að muna = that I need to remember

Together, they form the thing that I need to remember, or more naturally, what I need to remember.

After þurfa (to need / have to), Icelandic usually uses að before the infinitive.

So:

• ég þarf að muna
• literally: I need to remember

Here:

• þarf = present tense of þurfa
• að muna = to remember

This is similar to English need to remember.

More examples:

• Ég þarf að fara. = I need to go.
• Við þurfum að tala. = We need to talk.

Because þarf is the 1st person singular present tense form used with ég.

The verb is þurfa = to need. Its present tense forms include:

• ég þarf = I need
• þú þarft = you need
• hann/hún/það þarf = he/she/it needs
• við þurfum = we need
• þið þurfið = you (plural) need
• þeir/þær/þau þurfa = they need

So ég þarf is the correct form for I need.

Muna is the infinitive of the verb, meaning to remember.

It stays in the infinitive because it comes after þarf að:

• ég þarf að muna = I need to remember

This is similar to English, where we also use the base verb after need to.

A few examples:

• að muna = to remember
• að lesa = to read
• að sofa = to sleep

The colon introduces the specific thing that must be remembered.

So the sentence works like this:

• This is what I need to remember: one step at a time.

The part after the colon explains or summarizes the main idea. Icelandic punctuation here works much like English punctuation.

Because skref is a neuter noun, and the numeral/adjective must agree with it.

The word for one changes by gender:

• einn = masculine
• ein = feminine
• eitt = neuter

Since skref is neuter, you say:

• eitt skref = one step

Not:

• einn skref

It is in the nominative/accusative singular, and for this noun the form is skref.

In the expression eitt skref í einu, the phrase basically means one step at a time. After numerals like eitt, the noun appears in the expected singular form.

With neuter nouns like skref, the form often looks the same in nominative and accusative singular, so there is no visible change here.

Í einu is part of a fixed Icelandic expression meaning at a time.

So:

• eitt skref í einu
• literally: one step in one
• idiomatically: one step at a time

The word einu is the neuter dative form of einn/ein/eitt, because the preposition í often takes the dative when it expresses location or a figurative state rather than movement into something.

This whole phrase is best learned as a chunk:

• eitt í einu = one at a time
• dag einn í einu type patterns are less common, but the idea of X í einu as X at a time is very useful.

Because it follows the preposition í, and in this expression í takes the dative.

The neuter forms of one are:

• nominative/accusative: eitt
• dative: einu
• genitive: eins

So:

• eitt skref = one step
• í einu = in one / at one / at a time depending on context

This is a good example of Icelandic case showing up in everyday idioms.

Yes, definitely. It is a very natural phrase and worth learning as a chunk.

It means:

• one step at a time

Even if you can analyze the grammar, it is best to remember the entire expression as a set phrase. That will help you use it more naturally and recognize it quickly when you hear it.

A natural reading would usually give some emphasis to the key information:

• Þetta er það sem ég þarf að muna: eitt skref í einu.

A learner may especially want to watch these sounds:

• Þ in Þetta is like th in thing
• ð in það is like th in this
• ég is pronounced roughly like yeg with Icelandic vowel quality
• skref has a clear skr- cluster
• einu begins with the vowel sound ei, roughly like ay

The exact pronunciation can vary slightly by speaker, but the main grammatical point is that this is said as one complete thought, with a pause before or after the colon idea: ...að muna: eitt skref í einu.

Yes. A more literal translation would be:

• This is that which I need to remember: one step in one.

That sounds unnatural in English, but it helps show the Icelandic structure:

• Þetta er = This is
• það sem = that which / what
• ég þarf að muna = I need to remember
• eitt skref í einu = idiomatically one step at a time

This kind of literal breakdown is useful because Icelandic often builds ideas in a more visibly grammatical way than natural English does.