Learn Hardcore Swahili: Huduma katika taasisi hii ni nzuri. - The service at this institution is good.

Huduma (service, noun)
katika (in/at, preposition)
taasisi (institution, noun)
hii (this, proximal demonstrative)
ni (is, copulative verb)
nzuri (good, adjective)

What is the function of ni in this sentence? Is it like the English “to be”?

Yes. ni is the equative or copula in Swahili. It links a subject (or locative phrase) to a predicate, whether that predicate is a noun or an adjective. In descriptive sentences—when you’re saying something is something—you need ni. Without it, you’d have an incomplete sentence.

What exactly does katika do here? Can we use another word instead?

katika is a preposition meaning “in” or “at.” It introduces the location where the service takes place. You can replace it with ndani ya (“inside of”) if you want to emphasize the interior, e.g.
Huduma ndani ya taasisi hii ni nzuri.
But katika is more neutral and most common for “at/in.”

Why is the demonstrative hii placed after taasisi, and how do we know it’s hii and not hiyo or huyu?

In Swahili, demonstratives follow the noun they modify. taasisi belongs to noun class 9/10 (a loanword class with no prefix), so it takes the proximal demonstrative hii (“this”).

hii = this (near speaker, class 9/10)
hiyo = that (further away)
huyu = this person (class 1)

Why don’t we have a word for “the” before huduma? Swahili seems to have no articles.

Correct—Swahili has no definite or indefinite articles like “the” or “a.” A bare noun can be definite or indefinite based on context. So huduma can mean “service,” “the service,” or even “a service,” depending on what you already know or what you say next.

Could we rephrase this as Taasisi hii ina huduma nzuri? Would it mean the same?

Yes.
Taasisi hii ina huduma nzuri
literally means “This institution has good service.” Here ina is the verb “it has” (class 9 subject concord i- + -na). Both sentences communicate roughly the same idea. The original emphasizes that service is good; the rephrased one emphasizes that the institution possesses good service. The practical difference is minimal.

Does nzuri need to change to agree with huduma or any noun class?

After the copula ni, adjectives stay in their base form and don’t take agreement prefixes. So nzuri remains nzuri, even though huduma is class 9/10. (When adjectives are used attributively—directly before a noun—they sometimes take prefixes, but not after ni.)

How do you pronounce taasisi correctly? The double “a” looks tricky.

The double aa indicates a long vowel: /taː.si.si/. You hold the a sound slightly longer than a single a. Swahili stress is light and even, but a learner can give a small emphasis to the first syllable: TAA-si-si.