Ég setti fimmtíu litla miða á kassana í geymsluhólfinu svo ég fyndi allt hraðar.

It has two parts:

1. Ég setti fimmtíu litla miða á kassana í geymsluhólfinu
   = the main clause

2. svo ég fyndi allt hraðar
   = a purpose clause, meaning so that I would/could find everything faster

So the sentence is built like:

I put fifty small labels on the boxes in the storage compartment, so that I’d find everything faster.

Setti is the past tense of setja, which means to put, to place, or to set.

Here, ég setti means I put or I placed.

A useful thing to notice is that setti is the same form for both I and he/she/it in the past:

• ég setti = I put
• hann/hún/það setti = he/she/it put

Because miða is the accusative plural form of miði.

The verb setja takes a direct object, and direct objects are very often in the accusative. Here, the thing being put is fifty small labels, so miði has to appear in the accusative plural:

• nominative plural: miðar
• accusative plural: miða

So:

• miðar = labels, as a subject
• miða = labels, as an object

In this sentence, they are the object of setti, so miða is correct.

Because the adjective has to agree with miða in gender, number, and case.

The noun miði is:

• masculine
• plural
• accusative

So the adjective lítill has to match that, and the correct form is litla.

So:

• fimmtíu litla miða = fifty small labels

This is a very normal agreement pattern in Icelandic.

Because fimmtíu is one of the numerals that is normally indeclinable in modern Icelandic.

So fimmtíu stays fimmtíu no matter what role it plays in the sentence.

Also, after numbers like fimm, tíu, tuttugu, fimmtíu, the noun is normally plural:

• fimmtíu miðar
• fimmtíu miða in the accusative

So the number itself stays the same, while the noun changes form as needed.

This is a very common Icelandic pattern with prepositions like á and í.

These prepositions can take either:

• accusative for movement toward/onto/into something
• dative for location in/on something

In this sentence:

• á kassana uses the accusative because the labels are being put onto the boxes
• í geymsluhólfinu uses the dative because the boxes are already in the storage compartment

So the contrast is:

• setja miða á kassana = put labels onto the boxes
• kassarnir eru í geymsluhólfinu = the boxes are in the storage compartment

That motion-vs-location distinction is extremely important in Icelandic.

It is a compound noun.

It is built from:

• geymsla = storage
• hólf = compartment, cubby, section

So geymsluhólf means something like:

• storage compartment
• storage cubby
• storage bin/section

The form geymsluhólfinu is:

• singular
• definite = the storage compartment
• dative, because it follows í in a location meaning

So:

• geymsluhólf = storage compartment
• geymsluhólfið = the storage compartment
• í geymsluhólfinu = in the storage compartment

Here svo means so that.

It introduces a clause of purpose:

• svo ég fyndi allt hraðar = so that I would find everything faster

This is different from other uses of svo, which can also mean things like so, then, or thus depending on context.

In this sentence, the meaning is specifically:

• I did X so that Y would happen

Because fyndi is the past subjunctive of finna.

That is used here because the clause after svo expresses purpose/intended result, not a simple statement of fact.

Compare:

• ég fann = I found
  This is plain past indicative, describing something that actually happened.

• ég finn = I find / I am finding
  Present tense.

• ég fyndi = I would find / so that I could find
  This is the form used here.

So svo ég fyndi allt hraðar does not mean so I found everything faster as a simple factual past statement. It means more like:

• so that I would find everything faster
• so that I could find everything faster

English often uses would or could here, while Icelandic often uses the subjunctive.

Because Icelandic often expresses that idea through the subjunctive form itself, instead of adding a separate auxiliary like English would.

So:

• fyndi already carries the sense of something intended, hypothetical, or dependent on another action

That is why svo ég fyndi can be translated naturally as:

• so that I’d find
• so that I could find

even though there is no separate word equal to English would in the Icelandic sentence.

Allt here means everything.

It is the object of finna:

• finna allt = find everything

So the clause means:

• svo ég fyndi allt hraðar = so that I would find everything faster

A learner might wonder whether allt means something like completely here, but in this sentence it is best understood as the pronoun everything.

Because Icelandic word order often places a short object before an adverb.

So:

• fyndi allt hraðar literally looks like would find everything faster

That is normal Icelandic structure.

English can also do this:

• find everything faster

So there is nothing unusual in meaning here. It is simply:

• verb: fyndi
• object: allt
• adverb: hraðar

Because hraðar is the comparative adverb.

Here it modifies the verb fyndi:

• find faster not
• a faster thing

Compare:

• hratt = fast, quickly
• hraðar = faster, more quickly

But hraðari is an adjective form, used with nouns:

• hraðari bíll = a faster car

Since the sentence is talking about how the speaker would find things, Icelandic needs the adverb:

• hraðar

Because Icelandic does not have an indefinite article like English a/an.

So a bare noun can simply be indefinite:

• miði = a label / label
• miðar or miða = labels

Definiteness is shown when needed by the definite ending:

• kassana = the boxes
• geymsluhólfinu = the storage compartment

But miða is indefinite, so no separate word is needed.