Cuando el autobús frena, me agarro al pasamanos.

Because here cuando is being used as a conjunction meaning when.

• cuando = when in a sentence like When the bus brakes...
• cuándo = when? in a direct or indirect question

Examples:

• Cuando el autobús frena, me agarro al pasamanos. = When the bus brakes, I hold onto the handrail.
• ¿Cuándo frena el autobús? = When does the bus brake?

So in your sentence, no accent is needed.

Spanish often uses the present tense to talk about something habitual or generally true.

So this sentence means something like:

• Whenever the bus brakes, I hold onto the handrail
• When the bus brakes, I hold onto the handrail

It is not necessarily about one specific moment right now. It describes a usual reaction.

This is very natural in both Spanish and English:

• When it rains, I stay inside.
• Cuando llueve, me quedo dentro.

Because agarrarse a means to hold onto or to grab onto something.

The me is the reflexive pronoun, and it is part of the verb pattern here:

• agarrar = to grab
• agarrarse a algo = to hold onto something / grab onto something

So:

• Agarro el pasamanos = I grab the handrail
• Me agarro al pasamanos = I hold onto the handrail / I grab onto the handrail

In this sentence, the reflexive version sounds more natural because the idea is that you secure yourself by holding onto the handrail.

Because the verb expression is agarrarse a.

You do not just say me agarro el pasamanos in this meaning. You say:

• me agarro a algo = I hold onto something

So:

• me agarro a el pasamanos

Then Spanish contracts a + el into al:

• a el → al

That is why the sentence has:

• me agarro al pasamanos

Al is the contraction of a + el.

So:

• al pasamanos = to the handrail / onto the handrail

This contraction happens almost every time a is followed by el:

• Voy al centro = I go to the centre
• Miro al conductor = I look at the driver

The main exception is when el is part of a proper name, such as El Escorial.

Here pasamanos means handrail.

In this sentence it is singular:

• el pasamanos = the handrail
• al pasamanos = to the handrail / onto the handrail

A useful thing to know is that pasamanos has the same form in the singular and plural:

• el pasamanos
• los pasamanos

You tell whether it is singular or plural from the article:

• el = singular
• los = plural

Because frenar can be used normally without se to mean to brake or to slow down by braking.

So:

• El autobús frena = The bus brakes

Se frena can exist, but it is not the most neutral version here. It can sound more like it slows itself down or put a bit more focus on the change of state. In a simple everyday sentence like this, frena is the most natural choice.

In Spanish, articles are used more often than in English.

So where English might say:

• When the bus brakes...

Spanish naturally says:

• Cuando el autobús frena...

Leaving out the article here would sound incomplete.

Because the sentence starts with a subordinate clause:

• Cuando el autobús frena, ...

When this kind of time clause comes first, a comma is commonly used before the main clause:

• Cuando llego a casa, ceno.
• Si llueve, no salgo.

If you reverse the order, the comma is often omitted:

• Me agarro al pasamanos cuando el autobús frena.

Yes. That is completely correct.

Both versions mean the same thing:

• Cuando el autobús frena, me agarro al pasamanos.
• Me agarro al pasamanos cuando el autobús frena.

The difference is mainly one of emphasis and rhythm.

Starting with Cuando el autobús frena... highlights the situation first:

• When the bus brakes...

Starting with Me agarro al pasamanos... highlights your action first:

• I hold onto the handrail when the bus brakes.

Because this sentence describes something habitual or generally true.

With cuando, Spanish uses:

• indicative for habitual actions or things that actually happen
• subjunctive for future or uncertain events

Here it is habitual:

• Cuando el autobús frena, me agarro al pasamanos. = Whenever the bus brakes, I hold onto the handrail.

Compare that with a future idea:

• Cuando el autobús frene, me agarraré al pasamanos. = When the bus brakes, I will hold onto the handrail.

So the sentence uses the indicative because it describes a usual pattern.

It works in Spain, yes, and it sounds natural. In Spain, you might also hear:

• sujetarse al pasamanos = to hold onto the handrail
• cogerse al pasamanos = to grab onto the handrail

One useful note for learners: coger is very common in Spain, but in many parts of Latin America it can have a vulgar meaning, so agarrarse or sujetarse is often safer internationally.

So for Spain Spanish, me agarro al pasamanos is perfectly fine.

It is:

• first person singular = I
• present tense
• from the reflexive verb pattern agarrarse a

Full present-tense forms would be:

• me agarro = I hold on
• te agarras = you hold on
• se agarra = he/she/it holds on
• nos agarramos = we hold on
• os agarráis = you all hold on
• se agarran = they/you all hold on

So me agarro means I hold on / I grab on.

Yes, depending on context, but hold onto the handrail is usually the best interpretation here.

Because of the situation:

• the bus brakes
• you react for stability

So me agarro al pasamanos suggests:

• I hold onto the handrail
• I grab onto the handrail

If the sentence were just agarro el pasamanos, that would sound more like the physical action of grabbing the handrail itself. The reflexive me agarro al pasamanos focuses more on using it to steady yourself.