Nakasulat sa pisara ang paalala na dalhin ang takdang-aralin at ang bolpen bukas.

This is a very common Filipino word order pattern. The sentence begins with the state/location phrase:

• Nakasulat sa pisara = written on the board

Then it introduces what that written thing is:

• ang paalala = the reminder

So the structure is roughly:

• Nakasulat sa pisara ang paalala...
• literally: Written on the board is the reminder...

In natural English, we usually say The reminder is written on the board, but Filipino often puts the descriptive part first.

Nakasulat means written or in written form.

It comes from the root sulat (write).
Here, naka- shows a resulting state:

• sumulat = wrote / to write
• isulat = write it
• nakasulat = already written / in a written state

So Nakasulat sa pisara means something like It is written on the board or Written on the board.

Ang marks the topic of the sentence.

In this sentence, the thing being identified as written on the board is the reminder, so it gets ang:

• Nakasulat sa pisara ang paalala
• The reminder is written on the board

If you think of the sentence as answering What is written on the board?, the answer is ang paalala.

Sa pisara means on the board.

• sa = a location marker, often meaning in, at, on, to
• pisara = blackboard / board

So:

• sa pisara = on the board

This tells you where the reminder is written.

Here, na is a linker. It connects paalala (reminder) to the idea that follows it.

• ang paalala na dalhin ang takdang-aralin...
• the reminder to bring the homework...

So na is not the word that in a fully independent-clause sense; it is mainly linking the noun paalala to the following phrase/clause that describes its content.

You can think of it as:

• paalala na... = reminder that... / reminder to...

Dala is the root word meaning bring / carry.
Dalhin is a conjugated form built from that root.

In this sentence, dalhin is used in a dependent clause after paalala, giving the meaning:

• reminder to bring...

So:

• dalhin ang takdang-aralin at ang bolpen
• bring the homework and the pen

This form is very common in reminders, instructions, and commands.

Correct — the subject is not stated explicitly.

In Filipino, it is very common to leave out the subject when it is understood from context. In a school reminder like this, the implied subject is something like:

• you
• the students
• whoever is being addressed

So the sentence does not need to say ninyo or mo unless the speaker wants to be more specific.

Because dalhin is an object-focus form, the thing(s) being brought are marked with ang.

So we get:

• ang takdang-aralin
• ang bolpen

Both are things the listener is being told to bring.

Repeating ang before each noun makes the coordination clear:

• ang takdang-aralin at ang bolpen
• the homework and the pen

Takdang-aralin is the usual Filipino word for homework.

It is made up of:

• takda = assign / scheduled / prescribed
• aralin = lesson / study material

So the literal sense is something like assigned lesson/work, which became the standard word for homework.

No, bolpen is a borrowed word, adapted from English ballpen.

This is very normal in Filipino. Many everyday objects have borrowed or adapted names. So:

• bolpen = pen / ballpen

Depending on region or speaker, you may also hear English-influenced forms in casual speech.

Bukas means tomorrow here, and time expressions are often placed flexibly in Filipino.

So this sentence ends with:

• ...ang bolpen bukas
• ...the pen tomorrow

This sounds natural. You could also move time expressions earlier in many contexts, but placing bukas at the end is very common and smooth.

On its own, bukas can mean either:

• tomorrow
• open

But in this sentence, it clearly means tomorrow because it modifies the reminder about bringing things.

So:

• dalhin ... bukas = bring ... tomorrow

There is no real ambiguity in context.

It is a full sentence, but it also sounds very natural as a noticeboard or classroom reminder sentence.

It has a slightly formal or written feel because of words like:

• nakasulat
• paalala
• dalhin

So it works well for something a teacher wrote on the board.

Yes. That is a very useful literal breakdown:

• Nakasulat = Written
• sa pisara = on the board
• ang paalala = the reminder
• na dalhin = to bring / that [someone should] bring
• ang takdang-aralin at ang bolpen = the homework and the pen
• bukas = tomorrow

So a close literal translation is:

• Written on the board is the reminder to bring the homework and the pen tomorrow.

That literal version helps show the Filipino structure, even though the natural English translation may be phrased differently.