A reunião em que a senhora escolheu a data do curso foi no começo de agosto.

Em que introduces a relative clause and refers back to a reunião.

So:

• a reunião = the meeting
• em que a senhora escolheu... = in which you chose...

In natural English, you might say the meeting when..., the meeting where..., or the meeting in which.... Portuguese often uses preposition + que in cases like this.

Here, em is connected to reunião as the setting of the action: the choice happened in / at that meeting.

Yes. A reunião na qual a senhora escolheu a data do curso... is correct.

The difference is mostly style:

• em que = very common and natural
• na qual = a bit more formal or heavier

Both mean essentially the same thing here.

In careful standard Portuguese, no. The preposition is needed: em que.

So the standard form is:

• A reunião em que...

not:

• A reunião que...

Why? Because the idea is in that meeting or at that meeting, so Portuguese keeps the preposition.

In everyday speech, some people do drop prepositions in similar sentences, but for learners, em que is the safe and correct choice.

You may hear that in conversation, but em que is better here.

• onde is most clearly used for places
• reunião is an event, not a physical place

So:

• A reunião em que... = best standard choice
• A reunião onde... = common in speech, but less precise
• A reunião na qual... = also correct

A senhora is a polite/formal way to say you when speaking to a woman in Brazilian Portuguese.

Depending on context, it can also literally mean the lady or the woman, but very often it functions as a formal second-person form of address, similar to ma’am or formal you.

So in this sentence, it most likely means:

• you (formal, addressing a woman)

Because a senhora is grammatically treated as third person singular, even though it means you.

So Portuguese uses:

• a senhora escolheu
• a senhora quer
• a senhora pode

not:

• a senhora escolheste
• a senhora queres
• a senhora podes

This is very important in Brazilian Portuguese: formal address forms like o senhor and a senhora take third-person verb forms.

Because senhora is literally a noun, and in this polite expression the article is part of the standard form:

• a senhora
• o senhor

You should usually learn them as complete expressions, not as just senhora or senhor by themselves when they mean formal you.

It means the date of the course or more naturally in English, the course date.

Here:

• a data = the date
• do curso = de + o curso = of the course

Portuguese often links nouns with de where English might use a noun-noun structure:

• a data do curso = the course date
• o professor do curso = the course teacher
• o começo de agosto = the beginning of August

Do is a contraction:

• de + o = do

So:

• a data do curso = the date of the course

Portuguese very often contracts prepositions with articles:

• de + o = do
• de + a = da
• em + o = no
• em + a = na

This sentence has two contractions:

• do curso
• no começo

Foi is the past tense of ser, and here it means something like was or took place.

So:

• A reunião... foi no começo de agosto.
• literally: The meeting... was at the beginning of August.
• natural meaning: The meeting took place at the beginning of August.

In Portuguese, ser is commonly used with events to talk about when or where they happened.

You could say aconteceu, but it changes the tone a little.

• foi = very neutral, common with events
• aconteceu = emphasizes that the event happened/occurred

So both are possible, but foi is very natural here:

• A reunião foi no começo de agosto.
• A reunião aconteceu no começo de agosto.

The first is often simpler and more idiomatic in this kind of sentence.

It means at the beginning of August.

Breaking it down:

• no = em + o
• começo = beginning
• de agosto = of August

So literally it is in the beginning of August, but natural English is at the beginning of August.

Yes. No início de agosto is also correct.

The difference is small:

• no começo de agosto = very common, natural
• no início de agosto = also common, sometimes slightly more formal or precise

In most situations, either one works.

Because both actions are presented as completed past events.

• escolheu = chose
• foi = was / took place

This tense is the pretérito perfeito in Portuguese, and it is often used where English also uses the simple past.

The sentence refers to:

1. a completed act of choosing the date
2. a completed meeting that happened in August

Because em que a senhora escolheu a data do curso is a restrictive relative clause: it identifies which meeting we are talking about.

So the meaning is:

• the meeting in which you chose the course date

This clause is necessary information, so there is no comma.

If you added commas, it would sound like the meeting was already identified and the clause was just extra information, which is a different idea.

Yes, it sounds fairly formal or at least polite.

Two things contribute to that:

• a senhora = formal/polite you
• em que = standard, neat relative-clause structure

A more casual version might use você:

• A reunião em que você escolheu a data do curso foi no começo de agosto.

And in very informal speech, people may simplify the structure even more, though the original sentence is the best model for correct, polite Portuguese.