Ég tek verkjalyfið áður en ég fer að sofa.

Because tek is the form that matches ég.

• taka = to take, the dictionary form
• tek = I take, the 1st person singular present tense

So Ég tek means I take.

Yes, at least in the present tense it has a vowel change, so the form is not just a simple ending added to taka.

For example:

• ég tek = I take
• þú tekur = you take
• hann/hún/það tekur = he/she/it takes

So a learner often notices that a in taka becomes e in tek.

Because Icelandic very often builds compound nouns as a single word.

Here:

• verkja- = pain-related
• lyf = medicine, drug

Together, verkjalyf means pain medicine or painkiller. Then the ending -ið is added to mean the pain medicine.

So Icelandic writes the whole thing as one word: verkjalyfið.

That ending is the definite article, equivalent to English the.

Icelandic usually attaches the to the end of the noun instead of putting it in front.

So:

• verkjalyf = pain medicine / a painkiller
• verkjalyfið = the pain medicine / the painkiller

The ending -ið is the neuter singular definite ending here.

It is the direct object of tek, so it is in the accusative.

The verb taka normally takes an accusative object. In this sentence, the thing being taken is verkjalyfið.

A useful detail: for many neuter nouns in the singular, the nominative and accusative forms look the same, so you still see verkjalyfið.

Because áður en is the normal way to say before when it introduces a full clause.

Here it introduces:

ég fer að sofa = I go to sleep

So:

• áður by itself often means earlier or beforehand
• áður en = before
  • a clause

Also, en here is not the usual but. It is part of the fixed expression áður en.

Because en ég fer að sofa is its own clause, and that clause needs its own subject.

So Icelandic says:

• áður en ég fer að sofa = before I go to sleep

This works very much like English. You also repeat I in English, so Icelandic does the same.

Because Icelandic, like English, often uses the present tense for future-time meaning in clauses like this.

Compare English:

• I take the medicine before I go to sleep
• not usually before I will go to sleep

Icelandic does the same thing:

• áður en ég fer að sofa

So fer is present tense in form, but the time reference is understood from the context.

It means go to sleep or go to bed to sleep.

Literally:

• fer = go
• að sofa = to sleep

As a whole, fara að sofa is a very common expression.

A learner may wonder why it is not sef. The reason is that ég sef means I sleep / I am sleeping, while ég fer að sofa describes the action of going to sleep or going to bed.

So the difference is roughly:

• ég sef = I am sleeping / I sleep
• ég fer að sofa = I go to sleep / I go to bed

Here að marks the infinitive sofa, similar to English to in to sleep.

So:

• sofa = sleep, to sleep
• að sofa = to sleep, in this construction

In this sentence, it is part of the normal phrase fara að sofa.

Yes, but the meaning changes.

• verkjalyf = pain medicine / painkillers in a general or indefinite sense
• verkjalyfið = the pain medicine, a specific medicine already known in the situation

So if you mean a particular medicine, verkjalyfið is the natural choice.

Yes. Icelandic word order is flexible, but it still follows important rules.

The original sentence is:

Ég tek verkjalyfið áður en ég fer að sofa.

You can also put the time clause first:

Áður en ég fer að sofa tek ég verkjalyfið.

Notice what happens then:

• the clause áður en ég fer að sofa comes first
• the finite verb tek comes before the subject ég in the main clause

That is a normal Icelandic pattern.