יש הודעה ברמקול של התחנה, ולכן אנחנו מחכים עוד כמה דקות.

יש is the standard Hebrew way to say there is or there are. It introduces the existence of something.

So יש הודעה means there is an announcement.

A useful point: יש does not change for singular or plural: יש הודעה = there is an announcement
יש הודעות = there are announcements

Because the sentence is introducing something as new information: there is an announcement, not there is the announcement.

In this kind of sentence, Hebrew usually uses an indefinite noun when you are just saying that something exists or is happening. So יש הודעה sounds natural.

If you were talking about a specific, already known announcement, the phrasing would usually be different and the context would make it definite.

Because Hebrew ב־ does not only mean in. Depending on context, it can also mean something like on, through, or via.

With devices or communication channels, ב־ is very common: ברדיו = on the radio
בטלפון = on the phone / by phone
ברמקול = over the loudspeaker / through the loudspeaker

So even though the most literal translation might seem like in the loudspeaker, the natural English meaning is over the loudspeaker.

של means of or belonging to.

So רמקול של התחנה means the station’s loudspeaker or a loudspeaker of the station, depending on context.

התחנה has ה־ because it refers to a specific station: the one relevant in the situation, such as the station where the speakers are.

Modern Hebrew very often uses של to show possession, where English might use ’s: הספר של דני = Danny’s book
הרמקול של התחנה = the station’s loudspeaker

In normal Hebrew spelling without vowel marks, ברמקול can be ambiguous.

It can represent: בְּרמקול = in/through a loudspeaker
or
בָּרמקול = in/through the loudspeaker

The writing looks the same. In actual speech, the vowels would show the difference.

In this sentence, the meaning is clearly something like over the station loudspeaker, so the definite sense is very likely intended.

ולכן means and therefore, and so, or therefore.

It connects the first part of the sentence to the result: There is an announcement over the loudspeaker, therefore we are waiting a few more minutes.

You could often use אז in casual speech: יש הודעה ברמקול של התחנה, אז אנחנו מחכים עוד כמה דקות.

That sounds a bit more conversational. ולכן is a little more formal or more explicitly logical.

In the present tense, Hebrew verbs do not clearly mark person the way English verbs do. They mainly show gender and number.

מחכים means waiting in the masculine plural form, so it could mean: we are waiting
or
they are waiting

Adding אנחנו makes it clear that the subject is we.

So אנחנו מחכים is very natural and often helpful, even though English learners may expect the verb alone to be enough.

מחכים is the present-tense masculine plural form of לחכות, which means to wait.

Here are the basic present-tense forms: מחכה = waiting, masculine singular
מחכה = waiting, feminine singular in unpointed spelling too, but pronounced differently in careful speech/context
מחכים = waiting, masculine plural
מחכות = waiting, feminine plural

Because אנחנו can refer to a mixed group or an all-male group, מחכים is the default form here. If the speakers were all female, you would normally say אנחנו מחכות.

It can mean both, depending on context.

In a question: כמה דקות? = how many minutes?

In a statement like this one: כמה דקות = a few minutes or some minutes

So in עוד כמה דקות, כמה means a few.

This is very common in Hebrew, and context usually makes the meaning clear.

Here עוד means more or additional.

So: כמה דקות = a few minutes
עוד כמה דקות = a few more minutes

That is why the phrase means we are waiting a few more minutes.

A common learner confusion is that עוד can also mean still in other contexts: אני עוד כאן = I am still here

So עוד is a flexible word, and you have to read it from context.

Yes. Hebrew word order is fairly flexible, especially with connectors like לכן and אז.

This sentence is natural: יש הודעה ברמקול של התחנה, ולכן אנחנו מחכים עוד כמה דקות.

But you could also hear: יש הודעה ברמקול של התחנה, לכן אנחנו מחכים עוד כמה דקות.
יש הודעה ברמקול של התחנה, אז אנחנו מחכים עוד כמה דקות.

The version with ולכן is smooth and standard. The meaning stays basically the same.

Yes, הודעה ברמקול is natural and understandable.

Another very common expression is הודעה בכריזה, where כריזה means a public-address announcement system: יש הודעה בכריזה = there is an announcement on the PA system

So the sentence you have is good Hebrew, but learners may also encounter כריזה in similar situations, especially in stations, airports, and other public places.