When do we use "ce qui", "ce que", "ce dont" ?

In French, there are three different ways to express "what" in a sentence; one can use ce qui, ce que, or ce dont. To understand when to use which one it is helpful to look at three examples. 1) The sentence "I don’t understand what’s happening" translated into French is "Je ne comprends pas ce qui se passe." Here we use ce qui because "what" is the subject of the verb that follows. 2) The sentence "He doesn't understand what I am doing" translated into French is "Il ne comprend pas ce que je fais." Here we use ce que because "what" is the object of the verb that follows. Ce que can also become ce qu' when followed by a vowel (e.g. ce qu'il, ce qu'elle, ce qu'on).3) The sentence "I don't understand what he is talking about" translated into French is "Je ne comprends pas ce dont il parle." Here we use ce dont because the verb parler is followed by de (e.g. parler de la pluie et du beau temps, parler des joueurs de foot). To sum it up, we use ce qui when "what" is the subject of the verb that follows; ce que/ce qu' when "what" is the object of the verb that follows; ce dont when "what" is followed by a verb that uses de, du, or des.