Når appelsinene er modne, lager jeg juice og legger resten i kjøleskapet.

Here, når means when.

It is used for something that happens regularly, generally, or whenever the situation occurs:

• Når appelsinene er modne, ... = When the oranges are ripe, ...

A learner may compare it with:

• når = when
• hvis = if
• da = usually when about a specific event in the past

So this sentence sounds like a general routine or repeated situation, not a one-time past event.

Appelsinene is the definite plural form of appelsin:

• en appelsin = an orange
• appelsiner = oranges
• appelsinene = the oranges

So the sentence is talking about the oranges, not just oranges in general.

Because modne agrees with appelsinene, which is plural.

The adjective moden changes depending on grammar:

• en moden appelsin = a ripe orange
• et modent eple = a ripe apple
• modne appelsiner = ripe oranges

After er, the adjective still agrees with the noun:

• Appelsinene er modne = The oranges are ripe

So modne is used because the subject is plural.

This is because of Norwegian word order.

The first part, Når appelsinene er modne, is a subordinate clause placed first. After that, in the main clause, Norwegian follows the V2 rule: the finite verb comes in the second position.

So:

• Når appelsinene er modne, lager jeg juice.

Literally, the structure is:

• When the oranges are ripe, make I juice

That sounds wrong in English, but it is normal in Norwegian.

If the sentence started directly with the subject, then you would get:

• Jeg lager juice når appelsinene er modne.

Both are correct, but the word order changes depending on what comes first.

Because the sentence begins with a subordinate clause:

• Når appelsinene er modne, ...

In standard Norwegian, a subordinate clause placed before the main clause is normally followed by a comma.

So the comma helps show the break between:

• the time clause: Når appelsinene er modne
• the main clause: lager jeg juice og legger resten i kjøleskapet

Because juice here is being used as an uncountable substance, like water or milk in English.

So:

• lage juice = make juice

You would not normally say en juice here, because that would sound more like a juice as one drink/serving, depending on context.

In this sentence, the meaning is that the speaker makes orange juice as a substance, so no article is needed.

Resten means the rest or the remainder.

It comes from rest:

• en rest = a remainder / leftover part
• resten = the rest

In this sentence, resten refers to the remaining oranges or whatever is left after making juice.

So:

• legger resten i kjøleskapet = put the rest in the fridge

Norwegian often uses resten without repeating the noun if the meaning is already clear.

Legger is the natural verb for laying/putting something somewhere, especially when the object is thought of as being placed down.

• å legge = to lay / put

Other possibilities exist, but they are not exactly the same:

• sette is often used for setting something upright or placing something in position
• putte can mean put, but often sounds more like stick/put in

So legger resten i kjøleskapet is a very normal and natural choice.

Because kjøleskapet is the definite form:

• et kjøleskap = a fridge
• kjøleskapet = the fridge

In many everyday situations, Norwegian uses the definite form where English would also say the fridge, because it refers to a specific, known fridge — usually the one in the home.

So:

• i kjøleskapet = in the fridge

Norwegian often uses the present tense for things that are:

• habitual
• repeated
• generally true
• part of a routine

So this sentence means something like:

• When the oranges are ripe, I make juice and put the rest in the fridge.

It does not have to mean this is happening right now. It can describe what the speaker normally does whenever that situation occurs.

Because the subject jeg already applies to both verbs.

So:

• lager jeg juice og legger resten i kjøleskapet

means:

• I make juice and put the rest in the fridge

Norwegian, like English, often avoids repeating the subject when the same subject continues with another verb.

You could think of it as:

• lager jeg juice og [jeg] legger resten i kjøleskapet

but the second jeg is omitted because it is unnecessary.

In this sentence, appelsinene clearly means the oranges (the fruit).

In Norwegian, the fruit is appelsin. The color orange is usually oransje.

So:

• en appelsin = an orange (fruit)
• oransje = orange (color)

That helps avoid the ambiguity that English has with the word orange.

Yes, but it means something slightly different.

• Når appelsinene er modne = when the oranges are ripe
• Når appelsinene blir modne = when the oranges become ripe

So:

• er modne focuses on the state
• blir modne focuses more on the change into that state

In many contexts, both are possible, but er modne is very natural if you mean the time at which they are ripe and ready to use.