Mimi ninakula mahindi yaliyochemshwa nyumbani.

Because mimi adds emphasis or contrast.

• ninakula already contains the subject I
• mimi is the independent pronoun me / I

So:

• Ninakula mahindi... = a neutral I am eating maize...
• Mimi ninakula mahindi... = I am eating maize... / As for me, I am eating maize...

In many situations, mimi can be omitted.

Ninakula can be broken down like this:

• ni- = I
• -na- = present tense marker
• -kula = eat

So ni-na-kula literally means something like I-present-eat.

Depending on context, it can mean:

• I am eating
• I eat

Not always. In Swahili, -na- is the general present tense marker, so it can cover both:

• I am eating
• I eat

English forces you to choose more often than Swahili does. The exact meaning comes from context.

Mahindi usually means maize / corn.

It belongs to the ma-/ya- noun class group in Swahili, which often behaves like a plural class. Even when English treats something like corn as a mass noun, Swahili may use a noun from a plural noun class.

That is why later words referring to mahindi must agree with that noun class.

Because Swahili modifiers must agree with the noun class of the noun they describe.

Since mahindi is in the ma-/ya- class, the relative form begins with ya-.

So yaliyochemshwa is the form that agrees with mahindi.

If the noun belonged to a different class, this word would change to match it.

It is basically a relative construction meaning that were boiled.

A useful breakdown is:

• ya- = agreement with mahindi
• -li- = past
• -yo- = relative marker
• -chemshwa = be boiled

So mahindi yaliyochemshwa literally means maize that was boiled or boiled maize.

In natural English, we often turn this into an adjective-like phrase, but in Swahili it is built more like a relative clause inside one word.

• -chemsha = boil something
• -chemshwa = be boiled

The ending -w- is a passive marker.

So:

• amechemsha mahindi = he/she has boiled maize
• mahindi yamechemshwa = the maize has been boiled

In your sentence, the passive is used because the maize is the thing that received the action.

It works like an adjective in the sentence, but structurally it comes from a relative-clause idea.

So you can think of it in two ways:

• function: it describes mahindi
• structure: it means which were boiled

This is very common in Swahili. A single long word can do the job that English often does with that was..., which were..., and so on.

Nyumbani means at home or home in a locative sense.

It comes from nyumba meaning house/home, plus the locative ending -ni.

So Swahili often expresses location without a separate preposition like English at:

• nyumbani = at home
• shuleni = at school
• mezani = on the table / at the table depending on context

This can be a little ambiguous, and learners often notice that.

Because nyumbani comes right after yaliyochemshwa, it can naturally be understood as:

• maize that was boiled at home

But depending on context, someone might also understand the whole sentence as involving eating at home.

If you want to make at home clearly describe the eating, you might choose a different word order or add more context.

So this is a good example of how Swahili, like English, can sometimes leave attachment slightly open unless the context makes it obvious.

Swahili does not have articles like English the and a/an.

That means a sentence can simply say:

• ninakula mahindi = I am eating maize / the maize / some maize

Context tells you which English choice fits best.

If Swahili wants to be more specific, it often uses other tools, such as:

• demonstratives: haya mahindi = this/these maize/corn
• context
• word order
• extra descriptive phrases

Yes. Ninakula mahindi yaliyochemshwa nyumbani is perfectly correct.

Using mimi is optional here and usually adds one of these effects:

• emphasis
• contrast
• topic-setting

So both are grammatical, but they do not sound exactly the same in tone.