Nasza sekretarka jest dziś zajęta, bo przygotowuje dokumenty na spotkanie dyrektora.

Nasza means our and it must agree with the noun sekretarka.

• sekretarka is feminine singular
• so the possessive adjective is also feminine singular: nasza

Compare:

• nasz dyrektor = our director (masculine)
• nasza sekretarka = our secretary (feminine)
• nasze biuro = our office (neuter)

So this is basic adjective agreement.

Yes. Sekretarka means female secretary and is a feminine noun.

A few useful related forms:

• sekretarka = female secretary
• sekretarz = male secretary / secretary

In this sentence, the speaker is talking about a woman, so sekretarka is the natural choice.

Because zajęta must agree with sekretarka, which is feminine singular.

After jest (is), Polish often uses an adjective that agrees with the subject:

• On jest zajęty = He is busy
• Ona jest zajęta = She is busy
• Oni są zajęci = They are busy

So:

• sekretarka = feminine
• therefore zajęta = feminine form of busy

Dziś means today. It is basically the same as dzisiaj.

• dziś = today
• dzisiaj = today

The difference is mostly stylistic:

• dziś is a little shorter and often feels slightly more compact or natural in many sentences
• dzisiaj is also very common and completely normal

So jest dziś zajęta and jest dzisiaj zajęta both work.

Bo means because.

It is very common in everyday Polish and sounds natural in speech.
Ponieważ also means because, but it is usually a bit more formal or written-sounding.

So:

• Jest zajęta, bo przygotowuje dokumenty. = She is busy because she is preparing documents.
• Jest zajęta, ponieważ przygotowuje dokumenty. = same meaning, but slightly more formal

In this sentence, bo is the most natural conversational choice.

Przygotowuje is the 3rd person singular present tense form, meaning:

• he/she/it prepares
• or in context, is preparing

Here it refers to sekretarka, so:

• przygotowuje = she is preparing

This verb is imperfective, which is why it can describe an action in progress right now.

Useful comparison:

• przygotowywać = to be preparing / to prepare (imperfective)
• przygotować = to prepare, to get something prepared (perfective)

The form przygotowuje belongs to the imperfective side.

Dokumenty means documents and here it is the direct object of the verb przygotowuje.

She is preparing what?
→ dokumenty

So Polish uses the accusative plural.

For this noun, the accusative plural looks the same as the nominative plural:

• nominative: dokumenty
• accusative: dokumenty

That is very common with masculine inanimate nouns in Polish.

Here na means something like for in the sense of for an event / for a purpose.

So:

• przygotowuje dokumenty na spotkanie = she is preparing documents for the meeting

This is a very common Polish pattern:

• kupić coś na imprezę = to buy something for a party
• przygotować coś na egzamin = to prepare something for an exam
• zrobić coś na jutro = to do something for tomorrow

After na in this meaning, Polish uses the accusative, so we get spotkanie.

This is an important question, because the two expressions are similar but not identical.

• spotkanie dyrektora = the director’s meeting / a meeting of the director
• spotkanie z dyrektorem = a meeting with the director

In your sentence, dyrektora is in the genitive and depends on spotkanie. It shows that the meeting belongs to, is organized by, or is associated with the director.

So:

• dokumenty na spotkanie dyrektora = documents for the director’s meeting

If the idea were specifically a meeting with the director, Polish would normally say:

• dokumenty na spotkanie z dyrektorem

Because after another noun, Polish often uses the genitive to show a relationship like of the director or the director’s.

Base form:

• dyrektor = director

Genitive singular:

• dyrektora = of the director / the director’s

So:

• spotkanie dyrektora literally means meeting of the director

This noun-plus-genitive structure is very common in Polish:

• gabinet dyrektora = the director’s office
• samochód nauczyciela = the teacher’s car
• plan firmy = the company’s plan

Not completely. Polish word order is more flexible than English word order, although some versions sound more natural than others.

The given sentence:

• Nasza sekretarka jest dziś zajęta, bo przygotowuje dokumenty na spotkanie dyrektora.

is neutral and natural.

You could also move some parts for emphasis, for example:

• Dziś nasza sekretarka jest zajęta...
• Nasza sekretarka dziś jest zajęta...

These all mean roughly the same thing, but the emphasis changes slightly.

Still, the original version is a very good standard order for a learner to use.

Yes, very often.

Polish frequently drops subject pronouns and even explicit subjects when they are understood from context. So if everyone already knows who is being discussed, you could say:

• Jest dziś zajęta, bo przygotowuje dokumenty na spotkanie dyrektora.

However, keeping Nasza sekretarka is useful when:

• you want to introduce the person clearly
• you want to emphasize who is busy
• the context is not obvious yet

So both are possible, but the full version is clearer.