When should I use qui/que/ce qui/ce que?

Qui, que, ce qui and ce que are all relative pronouns. This means that they link a noun with a relative clause. 

Qui and que can be roughly translated as that/which

Ce qui and ce que work similarly to qui and que. (Ce) qui is followed by a conjugated verb and (ce) que is followed by a subject.

However ce qui and ce que are used to refer to an idea that has already been mentioned. 

E.g. Je ne suis pas d'accord avec ce qu'il a dit. 

REMEMBER : ONLY QUE ELIDES (BECOMES QU' WHEN FOLLOWED BY A VOWEL OR MUTE SOUND [H])