Umráðamaðurinn kemur í dag.

Because Icelandic often builds meanings by combining parts into a single noun.

In this word:

• umráð = control, charge, authority over something
• maður = man, person
• -inn = the

So:

• umráðamaður = a person in charge / administrator / custodian
• umráðamaðurinn = the person in charge / the administrator

This kind of compound noun is very common in Icelandic.

In Icelandic, the is usually added to the end of the noun as a suffix rather than written as a separate word.

So:

• umráðamaður = an administrator / a person in charge
• umráðamaðurinn = the administrator / the person in charge

The ending -inn here is the masculine singular nominative definite ending.

It is:

• masculine
• singular
• nominative
• definite

It is nominative because it is the subject of the sentence, the one doing the action:

• Umráðamaðurinn kemur í dag.
  = The administrator/person in charge comes today.

If the noun had a different role in the sentence, its form could change.

Not necessarily in actual meaning, but grammatically it is a masculine noun.

Historically, maður means man or person, and in compounds it often means person associated with something. So umráðamaður can refer to someone in charge, even though the word itself is grammatically masculine.

For a learner, the important thing is:

• treat umráðamaður as a masculine noun
• that affects articles, adjectives, and pronouns used with it

Because kemur is the conjugated form of the verb koma.

• koma = to come
• kemur = comes / is coming

Here the subject is third person singular, umráðamaðurinn, so the verb must match that:

• ég kem = I come
• þú kemur = you come
• hann / hún / það kemur = he / she / it comes

So:

• Umráðamaðurinn kemur = The administrator comes / is coming

Grammatically, kemur is present tense, but in Icelandic the present tense is often used for near-future events, just as English can do.

So Umráðamaðurinn kemur í dag can mean something like:

• The administrator comes today
• The administrator is coming today
• sometimes, depending on context, almost The administrator will come today

The exact English translation depends on context, but the Icelandic verb form itself is present.

Í dag is the standard Icelandic expression for today.

Literally, it is:

• í = in
• dag = day

But as a fixed expression, it simply means today.

So:

• kemur í dag = comes today / is coming today

This is a very common time expression in Icelandic.

Because after the preposition í in this time expression, the noun appears in a different case form.

The dictionary form is:

• dagur = day

But in í dag, the form is:

• dag

This is something you will see often in Icelandic: nouns change form depending on their grammatical role and on the preposition used.

For now, it is best to learn í dag as a whole expression meaning today.

Yes, in this sentence it is quite similar to English:

• Umráðamaðurinn = subject
• kemur = verb
• í dag = time expression

So the structure is:

• Subject + Verb + Time

However, Icelandic word order is more flexible than English, and main clauses often follow the verb-second pattern. For example, you could also say:

• Í dag kemur umráðamaðurinn.

That still means The administrator is coming today, but now í dag is emphasized more, and the verb kemur stays in second position.

A rough learner-friendly pronunciation is:

• Umráðamaðurinn ≈ um-ROW-tha-ma-thur-inn
• kemur ≈ KYEH-mur or KEH-mur
• í dag ≈ ee douwg

A few useful sound notes:

• ð is like the th in this
• í is a long ee
• á is like ow in now
• r is usually trilled or tapped

So the whole sentence is approximately:

• um-ROW-tha-ma-thur-inn KEH-mur ee douwg

The exact pronunciation will vary a bit by speaker, but that should get you close.