Learn Hardcore Hausa: A lambun nan muna da masara da wake. - In this garden we have maize and beans.

A – in / at
lambu-n – garden + definite suffix -n
nan – this / here (demonstrative placed after the noun)
→ lambun nan = this garden / the garden here
muna – we (progressive/continuous form: we are)
da – with / have (here it functions to show possession)
masara – corn / maize
da – and
wake – beans

So a fairly literal sense is:
In this garden we-are-with corn and beans.
Which is naturally translated: In this garden, we have corn and beans.

What does A mean here, and do I always need it before a place?

A is a preposition meaning in / at / on (location).

A lambu – in a garden
A gida – at home
A kasuwa – at the market

You use A before a noun when you want to express location in a basic way. Sometimes people say a cikin (in(side)) for extra clarity or emphasis:

A cikin lambu – inside the garden

In your sentence, A lambun nan simply means in this garden. Yes, a preposition like A (or a cikin) is normally needed to express in/at a place.

Why is it lambun and not lambu before nan?

Hausa adds a definite suffix before certain elements, including demonstratives like nan.

Basic noun: lambu – a garden
With definite suffix: lambu + n → lambun

Then the demonstrative comes after the noun:

lambun nan – this garden / the garden here

This pattern is common:

gida → gidan nan – this house
motà → motar nan – this car

So lambun is just lambu with the definite linker -n that appears before nan.

What exactly does nan mean, and how is it different from something like wancan?

nan is a proximal demonstrative, roughly this / here.

Placed after a noun with the linker:

lambun nan – this garden / the garden here
mutumin nan – this man

wancan is more like that (over there), a distal demonstrative:

lambun wancan or wancan lambu – that garden (over there)

So:

nan – close to the speaker (this / here)
wancan / can – farther away (that / there)

Can I move the place phrase to the end and say Muna da masara da wake a lambun nan?

Yes, that is also grammatical:

A lambun nan muna da masara da wake.
Muna da masara da wake a lambun nan.

Both mean In this garden, we have corn and beans.

Differences:

A lambun nan muna da ... – puts the location first, slightly emphasizing where.
Muna da ... a lambun nan – starts with we have, more neutral or emphasizing what you have.

In everyday speech, both orders are fine; Hausa often places time/place expressions either at the beginning or at the end of the clause.

What does muna mean, and how is it related to mu?

mu is the plain pronoun we.
muna is the progressive / continuous form for we:

mu – we
muna – we are (doing something)

Examples:

Mu mutane ne. – We are people. (plain mu)
Muna tafiya. – We are going / we are walking.

In your sentence:

muna da – literally we are with, which in Hausa expresses we have.

You normally do not need to say Mu muna da ... unless you want to emphasize we (as opposed to someone else). The simple Muna da ... is the normal form.

Why is da used twice, and does it always mean the same thing?

In this sentence, da appears with two related but slightly different roles:

muna da masara ...
- Here da functions as a possession marker:
  - muna da masara – we have corn
masara da wake
- Here da is a coordinating conjunction, meaning and:
  - masara da wake – corn and beans

In general, da can mean:

with: Yana da aboki. – He is with a friend.
have (via be with): Ina da kudi. – I have money.
and: masara da wake – corn and beans

Context tells you which function is intended.

Why is there no word like the or some before masara and wake?

Hausa usually does not use a separate word for the / a / some the way English does. Instead, it relies on:

bare nouns: masara, wake – (some) corn, (some) beans
context
demonstratives or other markers when needed: wannan masarar, wannan waken – this corn, these beans, etc.

So muna da masara da wake by itself can mean:

we have corn and beans
we have some corn and (some) beans

If you wanted to be very specific, you could add other words (like numerals or wani / wasu for a/ some with certain nouns), but for things like corn and beans the bare noun is natural.

Could I write or say munada as one word instead of muna da?

In careful, standard writing, muna da is written as two words:

muna da masara – we have corn

In informal writing and some dialects, you may see things squashed together (like munada), but for learning and for standard Hausa you should keep them separate:

muna (we are) + da (with / have)

How would I say the negative: In this garden, we do not have corn and beans?

To negate muna da (we have), you typically say ba mu da ...:

Ba mu da masara. – We do not have corn.

With your full sentence:

A lambun nan ba mu da masara da wake.
– In this garden, we do not have corn and beans.

Often speakers add a final ba for extra emphasis:

A lambun nan ba mu da masara da wake ba.

If you want to emphasize that you have neither corn nor beans, you can also use ko:

A lambun nan ba mu da masara ko wake.
– In this garden, we have neither corn nor beans.

How do I pronounce masara and wake, and is wake like the English word wake?

Pronunciation (simplified):

masara: ma‑sa‑ra
- all short vowels, stress usually on the first syllable: MA‑sa‑ra
wake: wa‑ke
- two syllables, both short vowels: WA‑ke
- it does not sound like English wake (one syllable); pronounce it more like WA-keh.

Also, wake here is beans (a food), not the English verb to wake.