Tidsnedtellingen begynner når startknappen trykkes.

Because Norwegian very often forms compound nouns by joining words together into one word.

• tid = time
• nedtelling = countdown
  So tidsnedtelling = time countdown / countdown timer depending on context.

And:

• start = start
• knapp = button
  So startknapp = start button.

This is much more common in Norwegian than in English. Where English often uses two separate words, Norwegian usually prefers one compound word.

The ending -en is the definite article for many masculine nouns in Norwegian. Instead of putting the in front, Norwegian often adds the definiteness to the end of the noun.

• en knapp = a button

• knappen = the button

• en tidsnedtelling = a countdown
• tidsnedtellingen = the countdown

So Norwegian often expresses the as a suffix rather than as a separate word.

Because in Norwegian, definiteness is usually built into the noun itself.

English says:

• the countdown
• the start button

Norwegian says:

• tidsnedtellingen
• startknappen

So the meaning of the is already included in the -en ending.

Trykkes is the passive form of trykke.

• å trykke = to press
• trykker = presses / is pressing
• trykkes = is pressed

So:

• startknappen trykkes = the start button is pressed

The -s passive is very common in Norwegian, especially in instructions, formal language, and neutral descriptions of processes.

This sentence is not saying someone presses the button directly. It focuses on the action happening to the button:

• active: Noen trykker startknappen = Someone presses the start button
• passive: Startknappen trykkes = The start button is pressed

Yes. Startknappen blir trykket is also possible, and it also means the start button is pressed.

There is often a small stylistic difference:

• trykkes = more compact, often more neutral or formal
• blir trykket = sometimes a bit more explicit or conversational

In a sentence like this, trykkes sounds very natural.

Når means when and is used here to introduce a time clause.

• Tidsnedtellingen begynner når startknappen trykkes.
• The countdown begins when the start button is pressed.

In Norwegian, når is commonly used for things that happen whenever something else happens, or for a general condition in time.

This sentence sounds like a general rule or instruction:

• whenever the start button is pressed, the countdown begins

Because tidsnedtellingen is the thing doing the action.

• Tidsnedtellingen begynner = The countdown begins

This is an active verb: the countdown begins.

By contrast, trykkes is passive because the button is receiving the action:

• startknappen trykkes = the start button is pressed

So the sentence contains:

• an active main verb: begynner
• a passive verb in the subordinate clause: trykkes

Yes, begynner is present tense.

• å begynne = to begin
• begynner = begins / is beginning

Norwegian often uses the present tense for:

• general truths
• instructions
• automatic processes
• things that happen as a rule

So Tidsnedtellingen begynner når startknappen trykkes is a natural way to describe how something works.

English does the same in many cases:

• The countdown begins when the start button is pressed.

Because når startknappen trykkes is a subordinate clause, and Norwegian subordinate clauses usually keep a more straightforward word order.

Here:

• startknappen = subject of the passive clause
• trykkes = verb

So the normal order is:

• når startknappen trykkes

If this were a main clause question, the order could be different, but here it is just a subordinate clause introduced by når.

Yes:

• Når startknappen trykkes, begynner tidsnedtellingen.

This means the same thing.

But notice the word order in the main clause after the opening subordinate clause:

• Når startknappen trykkes, begynner tidsnedtellingen.
• not Når startknappen trykkes, tidsnedtellingen begynner.

This is because Norwegian main clauses follow the V2 rule: the finite verb usually comes in the second position.

So after an opening clause like Når startknappen trykkes, the verb begynner comes before the subject tidsnedtellingen.

Yes, often it could.

• Tidsnedtellingen begynner
• Tidsnedtellingen starter

Both can work, and both can mean the countdown starts/begins.

A small nuance:

• begynner is often the more basic verb for begin
• starter can sound slightly more like starts up or starts

In this sentence, begynner sounds very natural and standard.

The full word can be broken down like this:

• tid = time
• nedtelling = countdown
• tidsnedtelling = time countdown / countdown
• tidsnedtellingen = the countdown

So the indefinite singular form is:

• en tidsnedtelling

And the definite singular form is:

• tidsnedtellingen

Yes. Knapp is normally a masculine noun:

• en knapp
• knappen

Since startknapp is built on knapp, it also behaves as a masculine noun:

• en startknapp
• startknappen

In Norwegian, the last part of a compound noun usually determines the grammatical gender and inflection. Here the last part is knapp.

It is a very typical instructional or technical statement explaining how something works.

Structure:

• Tidsnedtellingen begynner = main clause
• når startknappen trykkes = subordinate time clause

So the sentence pattern is:

[main action] + når + [triggering event]

This pattern is very common in manuals, interfaces, and descriptions of automatic processes.