jajeongeoreul tal ttaeneun helmeseul sseugo, jadongchareul tal ttaeneun anjeonbelteureul mae.

Because 를 is the object particle. The verb 타다 means to ride / to get in and use a vehicle, so the thing being ridden is marked as its object:

• 자전거를 타다 = to ride a bicycle
• 자동차를 타다 = to ride a car

In Korean, many vehicle expressions work this way with 타다.

Here, 타다 means to ride or to take a vehicle.

Common examples:

• 자전거를 타다 = ride a bicycle
• 버스를 타다 = take a bus
• 지하철을 타다 = take the subway
• 자동차를 타다 = ride in / take a car

So in this sentence, 탈 comes from 타다.

-ㄹ/을 때 means when.

So:

• 탈 때 = when riding / when you ride

It is attached to the verb stem:

• 타-
  • -ㄹ 때 → 탈 때

Because 타다 ends in a vowel, it takes -ㄹ 때.

A few more examples:

• 먹을 때 = when eating
• 갈 때 = when going
• 잘 때 = when sleeping

The 는 adds topic/contrast emphasis.

So 탈 때는 is roughly:

• when it comes to riding
• as for when you ride
• when you ride, ...

In this sentence, the speaker is contrasting two situations:

• 자전거를 탈 때는 ...
• 자동차를 탈 때는 ...

This gives the sentence a clear “in this case..., in that case...” structure.

Because Korean verbs change form before grammar endings.

The dictionary form is 타다, but before -ㄹ 때, it becomes 탈 때.

So this is just a normal conjugation:

• 타다 → 탈 때

It is similar to how English changes go into when going instead of keeping just go.

쓰고 comes from 쓰다, which here means to wear something on the head.

So:

• 헬멧을 쓰다 = to wear a helmet

The -고 means and, linking this action to the next part of the sentence.

So:

• 헬멧을 쓰고 = wear a helmet, and...

Korean uses different verbs for different kinds of wearing.

For things worn on the head, Korean usually uses 쓰다:

• 모자를 쓰다 = wear a hat
• 헬멧을 쓰다 = wear a helmet

This is different from English, where wear works for many kinds of clothing.

Because Korean often uses a specific verb depending on the item.

For belts, ties, and things you fasten around the body, Korean commonly uses 매다:

• 안전벨트를 매다 = fasten/wear a seatbelt
• 넥타이를 매다 = tie/wear a necktie
• 허리띠를 매다 = wear a belt

So 헬멧을 쓰다 and 안전벨트를 매다 are both natural, but they use different verbs because the items are worn in different ways.

매 is the plain style form here. It is not the polite ending.

So the sentence is written in a casual/plain style, which is common in:

• instructions
• slogans
• safety rules
• written advice
• textbook example sentences

Related forms:

• 매다 = dictionary form
• 매요 is actually not the normal polite form here
• 매어요 contracts to 매요 in theory, but in real use Koreans usually say 매다 in dictionary form or 매세요 / 맵니다 / 매요 depending on style and context; for seatbelts, 매세요 or 매십시오 is common in direct instructions
• 맵니다 = formal polite

In a safety-rule type sentence, the plain form 매 can sound like a concise instruction.

No. They are different verbs.

• 매다 = tie, fasten, wear a belt/seatbelt
• 맵다 = be spicy

They just happen to look similar in some forms.

Here, 매 comes from 매다, so it means fasten/wear.

-고 connects verbs and usually means and.

So:

• 헬멧을 쓰고, 자동차를 탈 때는...
  = wear a helmet, and when riding a car...

But in a sentence like this, -고 often feels more like a simple connection between instructions than a strict time sequence.

It links the first safety action to the second clause smoothly.

No. It is giving different advice for different situations:

• when riding a bicycle → wear a helmet
• when riding a car → fasten a seatbelt

The -고 simply connects the two pieces of advice in one sentence.

Korean often omits the subject when it is obvious from context.

In a general instruction sentence like this, the understood subject is something like:

• you
• one
• people

So the sentence naturally means something like:

• When riding a bicycle, wear a helmet, and when riding a car, fasten a seatbelt.

Korean does this very often.

자동차를 타다 is grammatical and clear, especially in textbook or formal language.

In everyday speech, many Koreans would more often say:

• 차를 타다 = ride in / take a car

So these are both possible:

• 자동차를 탈 때는 안전벨트를 매.
• 차를 탈 때는 안전벨트를 매.

The second one is usually more conversational.

Repeating it makes the contrast very clear and balanced:

• 자전거를 탈 때는 ...
• 자동차를 탈 때는 ...

This is a common Korean pattern. It helps separate the two cases neatly.

You could sometimes shorten repeated structures in Korean, but here the repetition sounds natural and is especially good for a teaching or instruction sentence.

It is better to think of it as a general rule or habitual instruction, not a simple present tense statement about what is happening right now.

The sentence means something like:

• When riding a bicycle, wear a helmet. When riding a car, fasten a seatbelt.

So it expresses general advice or a rule that applies whenever that situation happens.

Yes. That is often a very natural English translation.

Depending on context, it can mean:

• wear a seatbelt
• fasten a seatbelt
• buckle your seatbelt

In this sentence, fasten/buckle your seatbelt is especially natural because it is a safety instruction.

Yes. 쓰다 has multiple meanings.

Common ones include:

• to write
• to use
• to wear on the head

In this sentence, because the object is 헬멧, it clearly means to wear:

• 헬멧을 쓰다 = wear a helmet

Korean often has verbs with several meanings, and the object usually tells you which meaning is intended.