Kesho asubuhi, nitakwenda posta kutuma barua kwa dada yangu.

It is made of several parts:

• ni- = I
• -ta- = future tense marker, will
• kwenda = go

So nitakwenda means I will go.

One important thing for English speakers: Swahili often puts information that English expresses with separate words into a single verb form.

Because Swahili usually marks tense inside the verb itself.

In English, you say I will go with a separate helper word, will.
In Swahili, the future is shown by -ta- inside the verb:

• ninakwenda = I am going / I go
• nilikwenda = I went
• nitakwenda = I will go

So -ta- is doing the job of English will here.

Yes, in everyday use they are very close in meaning. Both can mean I will go.

You may hear both kwenda and kuenda / enda-based forms.
So:

• nitakwenda
• nitaenda

are both natural ways to say I will go.

For a learner, the important thing is to recognize both.

Swahili often combines time expressions very directly.

• kesho = tomorrow
• asubuhi = morning

So kesho asubuhi = tomorrow morning.

There is no need for a word like in or on. English often needs extra little words, but Swahili time expressions can simply stand on their own.

Because Swahili often does not use prepositions with common time expressions the way English does.

English says:

• tomorrow morning
• in the morning
• on Monday

Swahili often just uses the time word directly:

• kesho asubuhi
• Jumatatu
• saa mbili

So leaving out a preposition here is completely normal.

Posta usually means the post office or the postal service/postal place, depending on context.

In this sentence, kwenda posta most naturally means to go to the post office.

It is a very common word, and it behaves like a normal Swahili noun in the sentence.

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

So:

• posta can mean the post office or just post office
• barua can mean a letter, the letter, or just letter/mail, depending on context

Context tells you which meaning is intended.

Kutuma is the infinitive, meaning to send.

After a verb of movement like go, Swahili often uses the infinitive to show purpose:

• nitakwenda posta kutuma barua

This literally works like:

• I will go to the post office to send a letter

So kutuma answers the question for what purpose?
Why go to the post office? To send a letter.

Yes. That is a very helpful way to understand it.

The structure is:

• kwenda posta = go to the post office
• kutuma barua = to send a letter

Together, it expresses destination plus purpose:

• go to the post office to send a letter

This is a very common Swahili pattern.

Here it most naturally means a letter.

But barua is one of those nouns whose singular and plural forms are often the same in shape. Context tells you whether it means:

• a letter
• letters
• sometimes more generally mail

In this sentence, because the meaning is specific, it is understood as a letter.

Kwa is commonly used for meanings like to, for, at, or from, especially with people, depending on context.

Here it marks the recipient:

• kwa dada yangu = to my sister

So the sentence says the letter is being sent to the sister.

With people, kwa is very common in this kind of situation.

This is a great question, because it looks irregular to many learners.

With many nouns referring to people, you often see possessives like:

• mtoto wangu = my child
• rafiki yangu = my friend

But with some family and kinship terms, forms like yangu are very common:

• baba yangu = my father
• mama yangu = my mother
• dada yangu = my sister
• kaka yangu = my brother

So dada yangu is the normal expression here.

Some parts can move, but this order is very natural.

This sentence starts with the time expression:

• Kesho asubuhi, ...

That is similar to English Tomorrow morning, ...

You could sometimes place the time expression later, but putting it first is a very common way to set the scene. The rest of the sentence also follows a natural order:

1. time
2. main action
3. destination
4. purpose
5. recipient

So this sentence is a good model to copy.

In writing, the comma helps separate the time phrase from the rest of the sentence, much like in English:

• Tomorrow morning, I will go...

It is useful and natural in writing, but in speech the meaning is clear from intonation even without thinking about punctuation.

So the comma is not changing the grammar; it just makes the sentence easier to read.

A very useful pattern is:

• [time], ni-ta-VERB [place] ku-VERB [object] kwa [person]

Using this sentence:

• Kesho asubuhi, nitakwenda posta kutuma barua kwa dada yangu.

You can build similar sentences, for example:

• Kesho, nitaenda sokoni kununua matunda.
  Tomorrow, I will go to the market to buy fruit.

• Jioni, nitakwenda benki kutoa pesa.
  In the evening, I will go to the bank to withdraw money.

This makes the sentence a very useful grammar model, not just a single example.