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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