Ég set salat og brauð í matarkassann minn.

A word-by-word breakdown is:

• Ég = I
• set = put / place
• salat = salad
• og = and
• brauð = bread
• í = in / into
• matarkassann = the lunchbox / the food box
• minn = my

So the sentence literally looks like:

• I put salad and bread into the lunchbox my

But in natural English, that becomes I put salad and bread into my lunchbox.

Set is the 1st person singular present tense form of the verb setja, which means to put, to place, or to set.

A few useful forms are:

• að setja = to put
• ég set = I put
• þú setur = you put
• hann/hún/það setur = he/she/it puts

So Ég set ... means I put ... or I am putting ..., depending on context.

In this sentence, salat and brauð are being used in a general, indefinite way, like English salad and bread.

So:

• salat = salad
• brauð = bread

If you wanted to say the salad or the bread, Icelandic would usually add the definite article onto the noun itself.

For example:

• salatið = the salad
• brauðið = the bread

Here, the speaker just means they are putting some salad and bread into the lunchbox, not specifically the salad and the bread.

This is a very important Icelandic grammar point.

The preposition í can take:

• accusative when there is movement into something
• dative when something is already in something

In this sentence, the food is being put into the lunchbox, so Icelandic uses the accusative:

• í matarkassann = into the lunchbox

Compare:

• Ég set salat í matarkassann. = I put salad into the lunchbox.
• Salatið er í matarkassanum. = The salad is in the lunchbox.

So:

• -ann here shows the accusative definite singular
• -anum would be the dative definite singular

Matarkassann is made from:

• matur = food
• kassi = box

Together, matarkassi means food box or more naturally lunchbox.

Then Icelandic adds the definite article to the end of the noun:

• matarkassi = a lunchbox
• matarkassinn = the lunchbox (nominative)
• matarkassann = the lunchbox (accusative)

Because í here expresses movement, the noun is in the accusative, so we get matarkassann.

In Icelandic, possessive words like minn often come after the noun, especially when the noun is definite.

So:

• matarkassann minn = my lunchbox

This is very normal Icelandic word order.

English says:

• my lunchbox

But Icelandic often says the equivalent of:

• the lunchbox my

That sounds strange in English, but it is natural in Icelandic.

Minn has to agree with the noun it refers to in:

• gender
• number
• case

Here the noun is matarkassann, which is:

• masculine
• singular
• accusative

So the matching possessive form is:

• minn

A few related forms are:

• minn = masculine singular nominative/accusative in certain uses
• mínum = dative singular masculine/neuter
• mín = feminine singular or neuter plural in some contexts
• mitt = neuter singular

So minn is used because it matches matarkassann grammatically.

It is a very common and natural way, but Icelandic can also express possession in other ways depending on style and structure.

For learners, the most useful pattern is:

• definite noun + possessive
• matarkassann minn = my lunchbox

This is the pattern you will see very often in everyday Icelandic.

Yes, Icelandic word order is somewhat flexible, but Ég set salat og brauð í matarkassann minn is a completely normal neutral sentence.

You could change parts for emphasis, but the basic order here is straightforward:

• Ég = subject
• set = verb
• salat og brauð = object
• í matarkassann minn = prepositional phrase

For example, if you changed the order of the foods:

• Ég set brauð og salat í matarkassann minn.

That would still be correct; it just lists bread first instead of salad.

In this sentence, into is the better grammar explanation, because there is movement from outside to inside.

So although í is often glossed as in, here the meaning is really:

• into my lunchbox

That is exactly why the accusative is used after í in this sentence.

A rough learner-friendly pronunciation would be something like:

• yeg set sa-lat ohg broyth ee ma-tar-kas-an min

A few notes:

• Ég begins with a sound roughly like yeh/gyeh
• brauð has the Icelandic ð, a soft sound like the th in this
• í is a long ee
• nn in matarkassann is clearly pronounced

Pronunciation varies a bit by speaker, but that rough guide is enough to help you start saying it.