I am wondering on which occasions you use 'ki' in Creole. And when you are to say something like "He is the one that helps us" Do you use ki for 'that'? And is 'ke' also used for 'that'?

We are discouraged from using the relative pronoun "ke" in Creole.

You do not need to use "ke" unless you're speaking French.
This does not mean that Creole speakers won't attempt to use it.

Examples:
The dress that you bought is pretty.
Best way to say it: Rad ou achte a bèl.
What some will say: Rad ke ou achte a bèl.

This is the man that I saw.
Best way to say it: Sa se mesye mwen te wè a.
What some will say: Sa se mesye ke m te wè a.

He told me that he loves me.
Best way to say it:  Li di m li renmen m.
What some will say: Li di m ke l renmen m.

She didn't tell me that she was pregnant.
Best way to say it:  Li pa't di m li te ansent.
What some will say: Li pa't di m ke l te ansent.

The relative pronoun "ki" is used usually when it acts like a subject in a sentence.
Example:
The house that burned down was new.
Kay ki te boule a te nèf.

The girl who has the yellow dress is my daughter.
Ti fi ki gen rad jòn nan se piti fi mwen.

A man who has no eyes is blind.
Yon nèg ki pa gen zye avèg.

A house that is divided cannot stand.
Yon kay ki divize pa ka kanpe.

Foods that contain a lot of proteins are healthy.
Manje ki gen anpil pwoteyin bon pou lasante.

Rekative pronoun "ki"
Relative pronouns "ki" and "ke"
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"ki" or "sa" as "that" as the subject of a sentence?

I think you mean the relative pronoun.  Am I right?

The lady that was here.

Madanm ki te la a.

That's the car that hit me.

Sa se machin ki te frape m nan.

That is the boy who fell.

Sa se ti gason ki te tonbe a.

I want to buy the tallest tree.

I want to buy the tree that is the tallest.

Mwen vle achte pyebwa ki pi wo a.

Also check thess links:

http://sweetcoconuts.blogspot.com/2011/08/when-do-you-say-kisa-vs-kisa-ki.html

http://sweetcoconuts.blogspot.com/2011/08/so-there-are-two-ways-to-say-kisa-and.html

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Sak gen la

Sa'k gen la?
What's going on here?

Other ways to say "what's going on here?"

What's going on here?

Sa k genyen la?

Sa k'ap pase la?

Sa k'ap fèt la?

The letter "k" in the above sentences is a contraction for Creole relative pronoun "ki".

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Can you help me understand the difference between "okenn" and "anyen" and also between "ke" and "ki"? Mesi anpil! M renmen sit w!

Mèsi anpil!

Okenn is a determiner that stands for any, none, some, or an unspecified number.
It is usually placed in front of a noun.

It is not used in affirmative sentences such as: "You can have any car you want."  In the latter case, "any" will be translated as "nenpòt"

Example:
I don’t have any clothes.

Mwen pa gen okenn rad.

We don't see anyone here.

Nou pa wè okenn moun la.

There’s no students in the class.

Pa gen okenn elèv nan klas la.

He does have any respect for himself.

Li pa gen okenn respè pou tèt li.



Anyen stands for nothing and anything.
It does not need to be accompanied by a noun.
Example:

I don’t have anything.

M pa gen anyen.

There's nothing that can make me go back to your house.

Pa gen anyen ki ka fè m retounen lakay ou.

I can’t see anything.
M pa ka wè anyen.

He did not give me anything at all.

Li pat ban mwen anyen ditou.

I don't want anything to happen to you.
Mwen pa vle anyen rive w.

Let nothing scare you.
Pa kite anyen fè w pè.

Study hard so that nothing will keep you from passing your exams.
Etidye di pou anyen pa anpeche w pase egzamen yo.

Ki is translated in English as that, who, which

It refers to people, things or places.
It is the relative pronoun that acts as a subject before a verb.

Example:

I know the man who's standing at the door.

Mwen konnen mesye ki kanpe nan pòt la.

Do you know a school that is close to my house?

Eske ou konnen yon lekòl ki pre lakay mwen?

This is the church that burned down.

Sa se legliz ki te boule a?

This is the boy who sang at the parade.

Sa se ti gason ki te chante nan parad la.



Ke also means that.

Example:
I know that you love me.

Correct:  Mwen konnen ou renmen mwen.

Incorrect:  Mwen konnen ke ou renmen mwen

He told me that you went to the store.

Correct:  Li di mwen ou te ale nan magazen an.

Incorrect:  Li di mwen ke ou te ale nan magazen an.

The mango that you bought is spoiled.

Correct:  Mango ou achte a pouri.

Incorrect:  Mango ke ou te achte a pouri.

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can you un-contract sa kap fet! and break it down word by word please?

Sa kap fèt  → Kisa ki ap fèt

Sa - is contraction for kisa which means what.

Ki - is a relative pronoun that means that, who, or which

ap - is the determiner for the progressive tense

fèt (v.) - as a verb means to do, to happen, to occur

Kisa ki ap fèt? - literally means "what that happening?"

Kisa ki ap fèt? - is the expression for "what's happening?"
The verb to be (se) is not written in this expression. 

It is not required.

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Same goes for "sak pase?"

Sak pase? → Kisa ki pase?

literally "what that passed"

Sak pase? - is the expression for "what's going on?" "What is happening" "What is up?"

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