Oppryddingen begynner i kveld.

It is a noun meaning the cleanup or the tidying-up.

It comes from the verb phrase å rydde opp, which means to clean up / tidy up / clear away. From that, Norwegian forms the noun opprydding = cleanup / tidying-up. Then the definite ending is added:

• opprydding = cleanup
• oppryddingen = the cleanup

So the whole word is basically cleanup + the.

Because Norwegian often turns verb phrases into single-word nouns.

So:

• å rydde opp = to clean up
• opprydding = cleanup

This is very normal in Norwegian. English often keeps things more separate, but Norwegian frequently packs them into one compound word or derived noun.

The ending -en is the definite singular ending, so it works like the in English.

Compare:

• en opprydding = a cleanup
• oppryddingen = the cleanup

A learner often expects a separate word for the, but in Norwegian it is very often attached to the noun instead.

Also, with some nouns you may sometimes see a feminine definite form in -a, depending on style and dialect, but -en is completely normal in Bokmål.

Because Norwegian often uses the present tense for planned or expected future events, especially when there is a time expression like i kveld.

So begynner literally looks like begins, but in context it means:

• starts tonight
• is starting tonight

This is similar to English sentences like The meeting starts tonight or School begins tomorrow.

The infinitive is å begynne, meaning to begin.

So:

• å begynne = to begin
• begynner = begin / begins in the present tense

In this sentence:

• Oppryddingen begynner i kveld = The cleanup begins tonight

No. Norwegian verbs do not change for person the way English verbs sometimes do.

For example:

• jeg begynner = I begin
• du begynner = you begin
• han begynner = he begins
• vi begynner = we begin

The verb form stays begynner in all of these.

I kveld means tonight or this evening, depending on context.

Literally, i often means in, and kveld means evening, but as a fixed time expression i kveld is just the normal way to say tonight / this evening.

So in this sentence it tells you when the cleanup starts.

Because i kveld is the normal expression for tonight / this evening as a specific time.

På kvelden usually sounds more general, like in the evening or during the evening.

So:

• i kveld = tonight / this evening
• på kvelden = in the evening, often more general or descriptive

In this sentence, i kveld is the natural choice.

Yes. That is also correct.

Norwegian has a verb-second pattern, which means the finite verb usually stays in the second position. So if you move i kveld to the front, the verb must still come second:

• Oppryddingen begynner i kveld
• I kveld begynner oppryddingen

Both are correct, but the emphasis changes a little. The second version puts more focus on tonight.

Often yes:

• Oppryddingen starter i kveld

This would also be natural and understandable.

However, begynner is a very general and common word for begins/starts. Starter can sometimes feel a little more like starts up or gets going, though in many everyday sentences the difference is small. In this sentence, begynner sounds very standard and natural.

A rough guide is:

opp-RYD-ding-en

A few helpful notes:

• y in Norwegian is not like English y. It is a rounded vowel, a bit like German ü or French u.
• The dd does not mean you strongly pronounce two separate d sounds the way an English speaker might expect. It mainly shows that the vowel before it is short.
• The stress is mainly on rydd.

If you can say something close to opp-rüd-ding-en, you will be in the right area.