Qu'est-ce qu(e/i) or Quoi???

Question

I think I've finally gotten the "ce qui" vs "ce que" vs. "qui/e" down, but I'm utterly confused about when "quoi" is used.  When I see "what is," I invariably think "quoi," but I'm usually wrong.  The best rule I've determined is to use "quoi" with an infinitive, "je ne sais pas quoi faire," but is that really it for "quoi"?  Thanks!

Accepted Answer

Hi Rebecca, 
Just to add to the other answers, take a look at the following lesson -
Asking questions in French with "qui/que/quoi/quand/où/comment/pourquoi/combien" (French Question Words)
Hope it helps!

Answer

Salut Rebecca,https://www.wordreference.com/fren/quoiI think the above link with included further details toward the bottom of it, will provide you with all the variant uses of this pronoun/interjection.There has also been numerous similar queries answered here:-https://progress.lawlessfrench.com/questions/search?search=quoiBonne continuation Jim

Answer

Yes, that can be a bit tricky. Quoi is used in direct questions, those without a relative clause, since quoi can't function as a relative pronoun:
Vous savez quoi faire? -- Do you know what to do?Vous savez ce qu'il faut faire? -- Do you know what (that which) needs to be done?
Ils font quoi? -- What are they doing?Tu sais ce qu'ils font? -- Do you know what (that which) they are doing?Est-ce qu'ils font? -- What are they doing? (What is it that which they are doing?