Learn Hardcore Hausa: A makaranta dalibai da dama suna karatu yanzu. - At school many students are studying now.

If you want to explicitly mention the place, yes, you need a before makaranta.
Without it, Makaranta dalibai da dama suna karatu yanzu sounds odd or ungrammatical; makaranta would just sit there like a bare noun with no clear function.

Does A makaranta mean “at a school” or “at the school”? How is definiteness shown?

Hausa normally does not use separate words for “a” and “the” the way English does. A makaranta can mean:

at a school
at the school
at school (in a general sense)

The exact nuance (a vs. the) comes from context, not from the form of makaranta itself. Hausa signals definiteness more through:

context (what’s already known in the conversation),
sometimes possessives (a makarantar mu – “at our school”),
or demonstratives (a wannan makarantar – “at this school”).

Why does the sentence start with A makaranta? Could I put the place at the end instead?

Starting with A makaranta puts emphasis on the location: As for at school, many students are studying now.

You can also say:

Dalibai da dama suna karatu yanzu a makaranta.

Both are grammatical. The differences:

A makaranta, dalibai da dama suna karatu yanzu. (place is foregrounded; stylistically common, especially in narration or descriptive sentences)
Dalibai da dama suna karatu yanzu a makaranta. (focuses first on who is studying, and only then adds where)

So yes, you can move the place phrase to the end, but the sentence-initial position is very natural in Hausa when you’re setting the scene.

What exactly does dalibai da dama mean, and why is da there?

dalibai = students (plural of dalibi “student”)
da dama is a fixed expression meaning “many, numerous, plenty of.”

Literally, da often means “with/and”, and dama in other contexts can mean “opportunity / chance / possibility,” but in the idiom da dama it has evolved to mean “many / plenty”.

So dalibai da dama is best understood as “many students” or “a lot of students.” It’s a standard, very common way to say “many X”:

mutane da dama – many people
motoci da dama – many cars

How does dalibai mark plural? What is the singular form?

The singular is dalibi (student), and the plural is dalibai (students).

Hausa uses several different plural patterns, not just adding -s like English. Here:

dalibi → dalibai (the -i changes to -ai)

A few related examples of similar patterns:

bàbù → babban / manyan (different pattern)
malami (teacher) → malamai (teachers)

So, dalibai itself already shows plural; you don’t need an extra word like “many” to mark plurality, though you can add da dama to indicate “many” specifically.

What is suna doing here? Is it the verb “to be,” or is it a pronoun?

suna is a compound form:

su = they (3rd person plural pronoun)
na = a marker used for progressive / continuous aspect (“be doing”)

Combined, suna functions roughly like “they are (currently)” before another verb or verbal noun.

So, in:

dalibai da dama suna karatu,

suna is:

agreeing with the subject dalibai da dama (“they”),
and marking the action as ongoing / in progress (they are in the middle of studying/reading).

For other persons, this changes:

ina karatu – I am studying
kana karatu – you (m.sg.) are studying
kina karatu – you (f.sg.) are studying
yana karatu – he is studying
tana karatu – she is studying
muna karatu – we are studying
suna karatu – they are studying

Why is it karatu and not karanta? Is karatu a noun?

Yes, karatu is originally a verbal noun (like “reading / study / studies”), corresponding to the verb karanta (“to read / to study”).

In Hausa, it’s very common to express ongoing actions with:

a pronoun + aspect marker (like suna),
followed by a verbal noun:

Examples:

suna karatu – they are studying/reading
yana aiki – he is working (literally “he is work”)
muna jiran ka – we are waiting for you (with another verbal noun)

So suna karatu is literally “they are in (the state of) study/reading,” which corresponds to English “they are studying / they are reading.”
You wouldn’t normally say suna karanta in this structure; the natural form is suna karatu.

What does yanzu mean exactly, and does it always go at the end of the sentence?

yanzu means “now”. It’s an adverb of time.

Position:

In your sentence, … suna karatu yanzu is very natural: “they are studying now.”
You can also move it for emphasis or style:
- Yanzu, dalibai da dama suna karatu a makaranta.
- A makaranta yanzu, dalibai da dama suna karatu.

It most often appears:

at the end of the clause: … suna karatu yanzu
or at the beginning for emphasis: Yanzu dalibai da dama suna karatu…

Moving yanzu doesn’t usually change the basic meaning, just the emphasis or rhythm.

How would I say “Many students are not studying now” using this sentence as a model?

A natural Hausa negative version is:

A makaranta, dalibai da dama ba sa karatu yanzu.
= At school, many students are not studying now.

Key points:

ba … sa … ba is one common pattern for negating progressive-like actions:
- suna karatu → ba sa karatu (they are not studying)
The subject dalibai da dama stays the same.
The place and time expressions (A makaranta, yanzu) stay where they are, just like in the positive sentence.

So:

Positive: A makaranta dalibai da dama suna karatu yanzu.
Negative: A makaranta dalibai da dama ba sa karatu yanzu.

How does suna agree with dalibai da dama? What would the sentence look like with a single student instead?

suna is the 3rd person plural progressive form, matching the plural subject dalibai da dama (“many students”).

For a single student (dalibi), you need the 3rd person singular form yana:

A makaranta dalibi yana karatu yanzu.
= At school, a student is studying now.

You can see the pattern:

Singular: dalibi yana karatu – the student is studying
Plural: dalibai suna karatu – the students are studying

So the y-/s- at the start of yana / suna and the -na ending are part of a paradigm that changes with person and number.

Is A makaranta dalibai da dama suna karatu yanzu a natural, everyday kind of sentence, or does it sound formal or literary?

It is perfectly natural and everyday Hausa.

You might hear it (or very close variants) in conversation, in class, in radio commentary, etc., to describe what’s happening at a given time.
You could also slightly tweak it in speech, for example:
- Yanzu haka, a makaranta dalibai da dama suna karatu.
  (“Right now, at school, many students are studying.”)

But as it stands, A makaranta dalibai da dama suna karatu yanzu is a normal, idiomatic sentence for describing an ongoing situation at school.