Starfsmaðurinn afgreiðir endurgreiðsluna strax.

-inn is the suffixed definite article for a masculine singular noun in the nominative case.
So:

• starfsmaður = an employee
• starfsmaðurinn = the employee

Icelandic usually expresses the by attaching it to the end of the noun (rather than using a separate word like English the).

Because it’s the direct object of the verb afgreiðir and the verb afgreiða typically takes an accusative object. Also, it’s definite (the refund), so it takes the suffixed article too.

Breakdown:

• endurgreiðsla (feminine sg.) = a refund / reimbursement
• Accusative singular (indefinite): endurgreiðslu
• Accusative singular (definite): endurgreiðsluna = the refund

In this sentence:

• Starfsmaðurinn is the subject, so it’s in the nominative.
• endurgreiðsluna is the object, and afgreiða assigns accusative, so it’s in the accusative.

A lot of the time, case is shown by endings (and by the attached article), not by word order alone.

afgreiðir is:

• verb: afgreiða
• tense: present
• person/number: 3rd person singular (he/she/it)

So it matches starfsmaðurinn (one employee).
You can think of it as: (he/she) processes/handles.

afgreiða is more specific than a general do/make verb. It often means:

• to process (a request, transaction, refund)
• to handle / take care of (in a service or administrative sense)
• sometimes to serve (customers) or dispatch (orders), depending on context

So with endurgreiðsla, afgreiða is a natural “service-desk/admin” verb: processing the refund.

Placing strax at the end is very normal and neutral:
Starfsmaðurinn afgreiðir endurgreiðsluna strax.

You can also move it earlier for emphasis or style, for example:

• Starfsmaðurinn afgreiðir strax endurgreiðsluna. (still fine)

But the given order is probably the most straightforward for a simple statement.

Yes, it’s built from parts:

• endur- = again / back
• greiðsla = payment

So endurgreiðsla is literally something like “a paying back” → refund/reimbursement.

Key points:

• Stress is usually on the first syllable: STARF-smaður-inn, EN-dur-greiðs-lu-na, STRAX
• ð (in afgreiðir) is a voiced “th”-type sound, like in English this (not exactly identical, but close).
• æ (in afgreiðir) is roughly like the vowel in English eye in many accents.
• Final -ur in starfsmaður is often quite reduced in speech.

Approx. IPA (may vary by speaker):

• Starfsmaðurinn: /ˈstarfsˌmauðʏrɪn/
• afgreiðir: /ˈavˌkrɛiːðɪr/ (approx.)
• endurgreiðsluna: /ˈɛntʏrˌkrɛiːðs lʏna/ (approx.)
• strax: /straks/

• starfsmaður is masculine
• endurgreiðsla is feminine

Gender matters because it affects:

• the form of the definite article suffix (-inn, -in, -ið, etc.)
• case endings and adjective agreement (not shown here, but important in general)

Here you see it in:

• masculine nominative definite: starfsmaðurinn
• feminine accusative definite: endurgreiðsluna