Anna houdt de ladder vast terwijl Sofie bovenaan een schroef in de plank draait.

Because the full verb is vasthouden, which is a separable verb in Dutch.

• Infinitive: vasthouden = to hold onto / to hold steady
• In a main clause, it splits:
  • houdt = the conjugated verb
  • vast = the separable particle

So:

• Anna houdt de ladder vast.

This is very common in Dutch:

• opstaan → Ik sta op.
• meenemen → Zij neemt het mee.
• vastmaken → Hij maakt het vast.

But in some other structures, the parts stay together:

• Anna wil de ladder vasthouden.
• Dat is moeilijk vast te houden.

Because the subject is Anna, which is third person singular.

The verb houden is conjugated like this in the present tense:

• ik houd
• jij houdt
• hij/zij houdt
• wij houden
• jullie houden
• zij houden

So:

• Anna houdt
• Sofie draait

That final -t is very common for Dutch present tense verbs with he/she/it or a singular name.

By itself, vast can mean things like firm, fixed, stuck, or tight. In vasthouden, it adds the idea of holding something securely or steadily.

So de ladder vasthouden means more than just touching the ladder. It means:

• holding it steady
• keeping it from moving
• supporting it

In this sentence, Anna houdt de ladder vast suggests Anna is stabilizing the ladder while Sofie works.

Because ladder and plank are de-words in Dutch.

Dutch nouns usually take either:

• de
• het

These articles do not always match natural gender in English, so they usually have to be learned with the noun.

Here:

• de ladder = the ladder
• de plank = the plank/board

This is just part of the vocabulary you learn with each noun.

Terwijl means while.

It introduces a clause describing something happening at the same time:

• Anna houdt de ladder vast
• terwijl Sofie ... draait

So the structure is:

• one action in the main clause
• another simultaneous action in the clause introduced by terwijl

This is very similar to English while.

Examples:

• Ik kook terwijl zij de tafel dekt.
• Hij leest terwijl ik werk.

Because terwijl introduces a subordinate clause, and in Dutch subordinate clauses, the conjugated verb usually moves toward the end.

Main clause:

• Sofie draait een schroef in de plank.

Subordinate clause:

• terwijl Sofie een schroef in de plank draait

So after words like:

• terwijl = while
• omdat = because
• dat = that
• als = if/when

Dutch usually sends the verb to the end of the clause.

That is one of the most important Dutch word-order patterns to learn.

Bovenaan means at the top or at the upper end/top part.

In this sentence, it tells you where Sofie is in relation to the ladder or working area: she is up at the top.

Compare:

• boven = above / upstairs / up
• bovenaan = at the top

Examples:

• Zijn naam staat bovenaan de lijst. = His name is at the top of the list.
• Zij staat bovenaan de trap. = She is at the top of the stairs.

Here it works as an adverb describing Sofie’s position while she is screwing in the screw.

Because Dutch often uses een schroef in iets draaien for to screw a screw into something.

So:

• een schroef = a screw
• in de plank = into the plank/board

Literally, Dutch says something like turn a screw into the board.

This is idiomatic Dutch usage. English often uses drive or screw as the main verb:

• She screws a screw into the board.
• She drives a screw into the board.

Dutch uses draaien here because the action involves turning the screw.

Yes, its basic meaning is to turn or to rotate, but in the right context it can also be used for turning a screw into something.

So in general:

• draaien = to turn / rotate

But with een schroef:

• een schroef draaien
• een schroef in de muur/plank draaien

it means something like:

• turning a screw
• screwing a screw in

Dutch often relies on context here.

Because Dutch adverbs of place are often placed fairly early in the clause, before the object.

So this is natural Dutch word order:

• terwijl Sofie bovenaan een schroef in de plank draait

Here:

• Sofie = subject
• bovenaan = place/location adverb
• een schroef = object
• draait = verb at the end because of the subordinate clause

You could sometimes move elements around for emphasis, but this version sounds natural and neutral.

Because een introduces a screw, not the screw.

That usually means the screw is:

• not specifically identified yet
• just one screw among possible others
• not the main focus as a known object

So:

• een schroef = a screw
• de schroef = the screw

If both speaker and listener already knew exactly which screw was meant, de schroef could be possible in another context.

No, that word order is not natural in standard Dutch.

With a separable verb in a main clause, the normal pattern is:

• subject
• finite verb
• other elements
• separable particle at the end of the clause

So:

• Anna houdt de ladder vast.

Not:

• Anna houdt vast de ladder.

The particle vast belongs at the end of the main clause.

Yes, plank can mean board or plank, depending on context.

Common meanings include:

• a wooden board
• a shelf
• a plank

In this sentence, de plank is most naturally understood as a board/plank of wood that Sofie is putting a screw into.

So Dutch plank is a bit broader than English plank in everyday use.

Yes, some parts can move, but the grammar rules still apply.

For example, you could start with the terwijl clause:

• Terwijl Sofie bovenaan een schroef in de plank draait, houdt Anna de ladder vast.

That is also correct.

Notice what happens in the main clause after the subordinate clause comes first:

• houdt Anna instead of Anna houdt

This is because Dutch main clauses keep the finite verb in second position.

So both are correct:

• Anna houdt de ladder vast terwijl Sofie bovenaan een schroef in de plank draait.
• Terwijl Sofie bovenaan een schroef in de plank draait, houdt Anna de ladder vast.