Jeg legger boka på nattbordet før jeg slår av lampen.

Because legger is the present tense form of å legge (to lay / put).

• å legge = infinitive
• legger = present tense

Norwegian verbs are much simpler than English verbs in this respect. The verb form does not change depending on the subject:

• jeg legger
• du legger
• han legger
• vi legger

So jeg legger boka means I put/am putting the book down.

Because boka is the definite form: the book, not just a book.

With many Norwegian nouns, definiteness is added as an ending:

• ei bok = a book
• boka = the book

In this sentence, the speaker is talking about a specific book, so the definite form is used.

Also, bok is a feminine noun in Bokmål, so you often see:

• ei bok / boka

But it is also common in Bokmål to treat many feminine nouns as masculine:

• en bok / boken

So both boka and boken are possible in Bokmål.

Both are acceptable in Bokmål.

For the noun bok, you may see:

• ei bok – boka
• en bok – boken

The first option uses the feminine gender clearly. The second uses the common Bokmål pattern where feminine nouns can also take masculine forms.

So Jeg legger boka på nattbordet and Jeg legger boken på nattbordet are both fine. Boka may sound a little more natural or everyday to many speakers, but this can vary.

Because nattbordet means the nightstand.

• et nattbord = a nightstand
• nattbordet = the nightstand

Just like boka, this noun is definite. The sentence is referring to a specific nightstand, probably the one in the bedroom.

So:

• på nattbordet = on the nightstand
• på et nattbord = on a nightstand

På is the normal preposition for on in this context.

• på bordet = on the table
• på nattbordet = on the nightstand

The verb legge already tells you that something is being moved and placed somewhere, so på works naturally as onto/on.

English often distinguishes between on and onto, but Norwegian often just uses på.

Because å legge is the normal verb for laying/putting something down horizontally or placing it somewhere.

• å legge = to lay, put down
• å sette = to set, place upright / seat / put in a standing position
• å ta = to take

A book is normally something you legger on a table or nightstand.

So:

• jeg legger boka på nattbordet = I put the book on the nightstand

If you used setter, it would sound less natural here unless you were thinking of placing something upright in a special way.

Slår av is a phrasal verb / particle verb. The full verb is å slå av, which means to turn off in this context.

• å slå av lampen = to turn off the lamp

In main clauses, the verb and the particle are often split:

• Jeg slår av lampen
• Han slår av TV-en

So in your sentence:

• jeg slår av lampen = I turn off the lamp

This is similar to English verbs like turn off, where the meaning comes from the combination, not just the verb alone.

Historically, the pieces are related to meanings like strike or hit, but in modern Norwegian you should learn slå av here as a fixed expression meaning turn off.

So although it may look strange word-for-word, do not translate it literally. Just treat:

• slå av lyset
• slå av lampen
• slå av TV-en

as normal ways to say turn off the light/lamp/TV.

Because lampen is the definite form: the lamp.

• en lampe = a lamp
• lampen = the lamp

So the sentence refers to a specific lamp, not just any lamp.

This matches the rest of the sentence, where specific objects are being talked about:

• boka = the book
• nattbordet = the nightstand
• lampen = the lamp

Because før introduces a subordinate clause.

In Norwegian, main clauses usually follow the V2 rule, where the verb is in the second position. But subordinate clauses do not use that same pattern.

So:

• Main clause: Jeg legger boka på nattbordet
• Subordinate clause: før jeg slår av lampen

After før, the normal order is:

før + subject + verb

So før jeg slår av lampen is the expected word order.

Norwegian often uses the present tense for:

• habitual actions
• general statements
• near-future actions
• vivid descriptions of a sequence

So this sentence can sound like:

• something the speaker usually does before sleeping, or
• something the speaker is about to do now

English also sometimes does this:

• I put the book on the nightstand before I turn off the lamp

So the present tense here is completely normal.

In this sentence, før means before in time.

• før jeg slår av lampen = before I turn off the lamp

It can also appear in other contexts, but for learners the most important use is the time meaning:

• før middag = before dinner
• før jeg drar = before I leave

So here it connects two actions in a sequence.

Yes, it could:

• Jeg legger boka på nattbordet før jeg slår av lampen.
• Jeg legger boken på nattbordet før jeg slår av lampen.

The meaning does not change.

The difference is mainly style and gender choice in Bokmål:

• boka = feminine form
• boken = masculine-style alternative accepted in Bokmål

Many learners see both, so it is good to recognize them as equivalent here.

Yes. One of the most important features of Norwegian is that the definite article is often attached to the end of the noun instead of being a separate word like English the.

In this sentence you get:

• boka = the book
• nattbordet = the nightstand
• lampen = the lamp

That is very typical Norwegian.

So instead of using a separate word for the, Norwegian often builds definiteness directly into the noun.