Por poco pierdo el autobús de las ocho, pero la conductora esperó unos segundos.

Here por poco means almost or very nearly.

So:

• Por poco pierdo el autobús = I almost missed the bus

You could also say Casi pierdo el autobús, and the meaning is basically the same.

A useful nuance:

• casi is the most neutral, everyday word for almost
• por poco often feels a bit more vivid or dramatic, especially when something bad or inconvenient nearly happened

So por poco works very well here because missing the bus would have been a problem.

This is a very common learner question.

After por poco, Spanish often uses the present indicative to talk about something that almost happened in the past:

• Por poco me caigo = I almost fell
• Por poco pierdo el autobús = I almost missed the bus

So even though the event belongs to the past, the form after por poco is very often present in natural Spanish.

This is just an idiomatic pattern you need to get used to. In everyday Spanish, por poco pierdo... sounds very natural.

You may also hear:

• Por poco y pierdo el autobús

That means the same thing.

Yes, absolutely.

• Por poco pierdo el autobús de las ocho
• Casi pierdo el autobús de las ocho

Both are correct.

The difference is mostly in tone:

• casi = more neutral
• por poco = slightly stronger, more expressive, more like that was close!

El autobús de las ocho means the eight o’clock bus or the bus scheduled for eight.

The structure is very common in Spanish:

• el tren de las nueve = the nine o’clock train
• la clase de las diez = the ten o’clock class
• el vuelo de las siete = the seven o’clock flight

Here de las ocho identifies which bus it is.

If you said a las ocho, that would usually refer to when something happened, not which bus:

• Perdí el autobús a las ocho = I missed the bus at eight o’clock

That is different from:

• Perdí el autobús de las ocho = I missed the eight o’clock bus

Spanish normally uses the definite article when talking about clock time:

• la una
• las dos
• las ocho

So de las ocho literally means of the eight o’clock one.

This is standard Spanish time phrasing:

• Son las ocho
• el autobús de las ocho
• llego a las ocho

La conductora is the feminine form of el conductor.

So:

• el conductor = a male driver
• la conductora = a female driver

In this sentence, the driver is a woman, so conductora is the right word.

In Spain, conductor/conductora is a very normal and natural word for driver.
You might also hear other words in different contexts or countries, but la conductora is completely standard here.

Because it describes a completed action in the past.

• esperó unos segundos = she waited a few seconds

The preterite (esperó) is used because the action is seen as finished and limited: she waited, those few seconds passed, and the action ended.

If you used the imperfect (esperaba), it would sound more like background information or an ongoing past action, which is not the main idea here.

Because Spanish usually omits subject pronouns when the verb ending already shows who the subject is.

• esperó already tells you it is he/she/it in the past
• the context tells us it is la conductora

So la conductora esperó is perfectly natural.

You could say ella esperó, but that would usually add emphasis or contrast, for example:

• Todos querían irse, pero ella esperó unos segundos.

Unos segundos is the normal way to say a few seconds.

With short amounts of time, Spanish very often uses unos/unas:

• unos minutos
• unos días
• unos segundos

Algunos segundos is grammatically possible, but it sounds less natural here.
It can feel more literal or selective, whereas unos segundos is the everyday choice for an approximate small number.

Because in Spanish, a duration of time is usually expressed without a preposition:

• esperó unos segundos
• trabajé dos horas
• durmió diez minutos

So esperó unos segundos literally means she waited a few seconds.

Also, in standard Spanish from Spain, esperar usually does not need por before what is being waited for:

• esperar el autobús
• esperarme
• esperó unos segundos

Some varieties of Spanish do use esperar por, but that is not the usual pattern in Spain.

Because pero is connecting two full clauses:

• Por poco pierdo el autobús de las ocho
• pero la conductora esperó unos segundos

In Spanish, it is very common to put a comma before pero when it links two independent ideas like this.

So the punctuation is completely standard.

Yes, and that slightly changes the focus.

• La conductora esperó unos segundos = The driver waited a few seconds
• La conductora me esperó unos segundos = The driver waited a few seconds for me

Adding me makes it explicit that she waited for me specifically.
Without me, the sentence is still perfectly understandable from context.