Houd het stuur stevig vast als je door deze scherpe bocht rijdt.

Houd is the informal singular imperative of houden, so it means hold!

In Dutch, commands often use the verb stem:

• houden → houd
• komen → kom
• rijden → rij

So:

• Houd het stuur stevig vast. = Hold the steering wheel firmly.

If you added je, it would no longer be a command:

• Je houdt het stuur vast. = You hold the steering wheel.

So houd here is used because the speaker is directly telling someone what to do.

Because vasthouden is a separable verb.

The full verb is:

• vasthouden = to hold on to / to hold tight

In a main clause, separable verbs split apart:

• Ik houd het stuur vast.
• Houd het stuur vast.

So in your sentence:

• Houd ... vast

That is completely normal Dutch word order for a separable verb.

Compare:

• Ik sta op. = I get up.
  from opstaan
• Hij trekt zijn jas aan. = He puts on his coat.
  from aantrekken

Together, stevig vast means something like firmly / tightly / securely.

• vast already gives the idea of holding on
• stevig adds the idea of firmness or strength

So:

• iets vasthouden = to hold something
• iets stevig vasthouden = to hold something firmly
• iets stevig vasthouden = same idea

In this sentence, stevig strengthens the instruction. It sounds natural in Dutch, much like English hold it firmly or hold on tight.

Because stuur is a het-word in Dutch.

So you say:

• het stuur = the steering wheel

This is something you simply have to learn with the noun. Dutch nouns take either de or het:

• de bocht
• het stuur

A learner may want to memorize nouns together with their article:

• het stuur
• de bocht

That makes later grammar much easier.

Because bocht is a de-word, so the correct demonstrative is deze.

Dutch uses:

• deze with de-words
• dit with het-words

So:

• de bocht → deze bocht
• het stuur → dit stuur

Also, the adjective gets -e here:

• scherpe bocht

That is the normal form before a noun in this kind of phrase.

Dutch adjectives usually take -e when they come before a noun.

So:

• de scherpe bocht = the sharp bend
• deze scherpe bocht = this sharp bend

The basic adjective is:

• scherp = sharp

But before bocht, it becomes:

• scherpe

This is one of the most common adjective patterns in Dutch.

Because als introduces a subordinate clause, and in Dutch subordinate clauses the conjugated verb usually goes to the end.

So:

• main clause: Je rijdt door deze scherpe bocht.
• subordinate clause: als je door deze scherpe bocht rijdt

That is why the sentence is:

• Houd het stuur stevig vast als je door deze scherpe bocht rijdt.

Compare:

• Ik blijf thuis als het regent.
• Ze belt je wanneer ze aankomt.

This verb-final pattern is very important in Dutch.

Because the verb is rijden and the subject is je.

Present tense of rijden:

• ik rijd
• jij/je rijdt
• hij rijdt
• wij rijden

So in this sentence:

• je rijdt = you drive / you are driving

The -t ending is the normal ending for jij/je in the present tense.

The spelling looks a bit tricky because the stem is rijd-, and then Dutch adds -t, giving rijdt.

Literally, it is something like to drive through this sharp bend/curve.

• door = through
• bocht = bend / curve / turn
• rijden = to drive / ride

In English, we often say go around a bend or take a sharp turn, but Dutch commonly uses door een bocht rijden.

So although through may sound a bit unusual in very literal English, it is normal Dutch.

Here als is best understood as when or if in a practical instruction.

• Houd het stuur stevig vast als je door deze scherpe bocht rijdt.

This means something like:

• Hold the steering wheel firmly when you drive through this sharp bend.

In instructional contexts, als often works well where English might use when.

Could you use wanneer? Sometimes yes, but als is very common and natural here.

More or less, yes. Bocht is a broad word for a bend, curve, or turn in a road.

Depending on context, English translations could be:

• sharp bend
• sharp curve
• sharp turn

In this sentence, scherpe bocht suggests a road that curves sharply, so sharp bend or sharp turn both work well.

In a dictionary form, yes:

• vasthouden = to hold on to

But in this sentence, no, because the verb is conjugated in a main clause command, so it must split:

• dictionary form: vasthouden
• command: Houd ... vast

So you would not write:

• Houd het stuur stevig vasthoud ❌
• Houd het stuur stevig vasthouden ❌

The correct form is:

• Houd het stuur stevig vast.