Dhana hii ni muhimu.

A word-for-word breakdown is:

• dhana = idea, concept, notion
• hii = this
• ni = is / is being (the basic linking verb here)
• muhimu = important

So the structure is literally concept this is important. That is normal Swahili word order.

In Swahili, demonstratives like this and that usually come after the noun, not before it.

So:

• dhana hii = this concept
• not normally hii dhana

This is one of the first word-order differences English speakers notice. English says this concept, but Swahili usually says concept this.

Here, ni works like the English linking verb is. It connects the subject dhana hii with the description muhimu.

So:

• Dhana hii ni muhimu = This concept is important.

It is very often translated as is, but it is better to think of it as a general copula/linking word used to connect one thing with another description or identity.

Dhana belongs to the N class (often called class 9/10), and the demonstrative has to match that noun class.

For this noun class:

• singular this = hii
• plural these = hizi

So:

• dhana hii = this concept
• dhana hizi = these concepts

Even if noun classes are new to you, the main practical point is: the form of this/these changes depending on the noun.

Because muhimu is one of the adjectives that usually stays the same across noun classes. It does not normally take different agreement prefixes.

So you can have:

• dhana hii ni muhimu = this concept is important
• wazo hili ni muhimu = this idea is important
• mawazo haya ni muhimu = these ideas are important

In all of these, muhimu stays muhimu.

A simple pronunciation guide is:

• dhana ≈ DHA-na
  The dh is like the th in this.
• hii ≈ hee-ee
  Try to pronounce both i vowels, not like English high.
• ni ≈ nee
• muhimu ≈ moo-HEE-moo

So the whole sentence is roughly:

DHA-na hee-ee nee moo-HEE-moo

Yes. Dhana is one of those nouns whose singular and plural often have the same basic form. The demonstrative or other words in the sentence help show whether it is singular or plural.

Compare:

• dhana hii ni muhimu = this concept is important
• dhana hizi ni muhimu = these concepts are important

So the change from singular to plural shows up in hii → hizi, not usually in dhana itself.

In a normal, neutral sentence like this, you should keep ni.

So the standard form is:

• Dhana hii ni muhimu

Leaving out ni would sound incomplete or nonstandard in most ordinary learner contexts. As a beginner, it is safest to use ni when you want to say something like X is important, X is big, X is a teacher, and so on.

You can change the demonstrative or add an adverb:

• Dhana hiyo ni muhimu = That concept is important.
• Dhana hii ni muhimu sana = This concept is very important.

Here:

• hiyo = that
• sana = very

So sana is an easy way to strengthen an adjective like muhimu.