Learn Hardcore Swahili: Niletee penseli, tafadhali.

It’s the object marker for first person singular, meaning me. Swahili allows object markers on positive imperatives, so ni-letee is literally “bring (for) me.”

Why is it letee and not lete or leta?

leta is the base/dictionary form “to bring,” not the imperative.
lete is the 2nd person singular imperative “bring!”
letee is the imperative of letea “bring for/to (someone).” The applicative -ea contracts to -ee in the imperative: letea → letee. Since you’re bringing something to someone (me), you use the applicative: ni-letee “bring (it) for me.”

Can I say Nilete penseli instead?

No. Without the applicative, ni- would be the direct object (me), giving the odd meaning “bring me (as the thing).” To say “bring me a pencil,” use the applicative: Niletee penseli. Alternatives:

Letea mimi penseli = bring a pencil to me.
Lete penseli = bring a pencil (recipient left to context).

Can I drop ni- and just say Lete penseli, tafadhali?

Yes. That politely tells someone to bring a pencil, but it doesn’t explicitly say “to me.” If you need to make the recipient explicit, use niletee or add mimi: Letea mimi penseli.

How do I say this to more than one person?

Use the plural imperative ending -ni: Ni-letee-ni → Nileteeni penseli, tafadhali.

Where can I put tafadhali, and do I need the comma?

You can put tafadhali at the start or the end; the comma is stylistic:

Tafadhali niletee penseli.
Niletee penseli, tafadhali.
Tafadhali, niletee penseli.

What’s the plural of penseli? How do I say “a pencil” vs “pencils”?

Penseli is a class 9/10 loanword; singular and plural look the same. Context or numbers show plurality:

“a pencil” → penseli (optionally penseli moja for clarity)
“pencils” → penseli (or with a number: penseli mbili, “two pencils”)

How do I say “the pencil” or “that pencil”?

Swahili has no articles; use demonstratives:

hii penseli / penseli hii = this pencil
ile penseli / penseli ile = that pencil

Why is there no word for you in the sentence?

Positive imperatives in Swahili omit the subject prefix. The addressee (“you”) is understood. In the negative, you do add it:

sg: usi- … Usiniletee penseli.
pl: msi- … Msiniletee penseli.

How can I make the request softer or more polite?

Common options:

Naomba penseli. (I’m requesting a pencil.)
Naomba uniletee penseli.
Unaweza kuniletea penseli, tafadhali? (Could you bring me a pencil, please?) You can keep tafadhali wherever it sounds natural.

Can I use samahani instead of tafadhali?

Samahani means “excuse me/sorry.” It’s fine to get attention or preface a request, often together with tafadhali:

Samahani, tafadhali niletee penseli.

Is kalamu a good word for “pencil”?

Today kalamu usually means “pen” (or a writing instrument in some contexts). Penseli is the standard, unambiguous word for “pencil.”

If I name the recipient instead of using ni-, what word order do I use?

Put the recipient before the thing:

Mletee Asha penseli. = Bring Asha a pencil. You normally wouldn’t also add an object marker for Asha in such a simple sentence.

How do I say “Don’t bring me a pencil, please”?

To one person: Usiniletee penseli, tafadhali.
To several people: Msiniletee penseli, tafadhali.

How do I pronounce the sentence?

Niletee: ni-le-TEE (stress on the second-to-last syllable)
penseli: pen-SE-li (stress on SE)
tafadhali: ta-fa-DHA-li (stress on DHA; dh is like the English “th” in “this”)