Ég les bók í smástund áður en ég fer að sofa.

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

So:

• bók = a book or just book
• bókin = the book

The definite article is usually attached to the end of the noun, not written as a separate word.

Lesa is the infinitive, meaning to read.

When the verb is conjugated for ég = I, it becomes les in the present tense:

• ég les = I read
• að lesa = to read

So les is just the correct present-tense form for ég.

It can often cover both ideas, depending on context.

In Icelandic, the simple present is broader than in English. So ég les may mean:

• I read
• I am reading

In this sentence, it most naturally sounds like a habitual or regular action: reading for a little while before going to sleep.

If you really want to emphasize an ongoing action right now, Icelandic often uses:

• ég er að lesa = I am reading

It actually is in the accusative case here, because lesa takes a direct object in the accusative.

However, for the noun bók, the nominative and accusative singular happen to look the same:

• nominative: bók
• accusative: bók

So the case is there grammatically, but you do not see a visible change in this form.

It means for a short while, for a little while, or briefly.

• smá- = small, little
• stund = a while, a moment, a period of time
• smástund = a short while

So í smástund is a very natural time expression meaning that the action lasts for a short period.

Because í smástund is an established Icelandic expression for duration.

English uses for in for a little while, but Icelandic uses í here. This is one of those places where you should learn the whole phrase rather than translate word for word.

So it is best to remember:

• í smástund = for a little while

Áður en means before when it introduces a whole clause.

So:

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

It is a conjunction that connects the main clause to a subordinate clause.

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

Compare English:

• I read for a while before I go to sleep

English also repeats I, and Icelandic does the same:

• áður en ég fer að sofa

Because after a subordinating conjunction like áður en, Icelandic normally uses subordinate-clause word order.

That means the subject usually comes before the finite verb:

• áður en ég fer

This is different from the verb-second pattern that often appears in main clauses.

That is normal in Icelandic.

Just like English says:

• before I go to sleep

Icelandic also uses the present tense for something that is still in the future relative to the first action:

• áður en ég fer að sofa

So even though the going-to-sleep happens later, the present tense is the natural choice.

Literally, it is something like go to sleep.

• fer = go
• að sofa = to sleep

As a whole, fara að sofa is a common expression meaning:

• go to sleep
• go to bed, depending on context

It is a very natural everyday phrase.

Að is the infinitive marker, like English to.

So:

• sofa = sleep
• að sofa = to sleep

In this expression, Icelandic uses fara að sofa, so you should learn it as a set phrase.

Not exactly.

• fara að sofa = go to bed / go to sleep
• sofna = fall asleep

So fara að sofa is about beginning the bedtime action or going off to sleep, while sofna focuses more on the moment of actually falling asleep.

Yes, but the meaning changes.

• Ég les bók = I read a book
• Ég les bókina = I read the book

Use bókina when you mean a specific book that is known from context. Use bók when it is nonspecific.

Yes, but it is slightly different.

• les bók usually means read a book
• les í bók often means read in a book, read from a book, or read through a book / look in a book

So in your sentence, les bók is the most straightforward way to say that you spend some time reading a book before sleep.