How do i use french interrogative pronouns?

Qui is used to ask about who or whom. 
Que is used to ask about what (ideas or things). It changes to Quoi after preposition.

Qui, -> Who/whom
que, -> What with a verb after
quoi, -> Also what with a verb after but you use it when there is a preposition before (de, à, sur, sous, en, pou)
Que penses-tu ?// À quoi tu penses?
(Also Que is only use as the first word of a sentence and quoi is used everywhere else)
lequel(masculin)/laquelle(féminin)> Which one
quel(masculin) and Quelle(féminin)-> What but when there is a noun after

A qui-> Whose
A quoi -> To What (What/To what are you thinking. About/ A quoi penses-tu )

Quand -> When

It’s pretty much everything but I don’t know if I explained it correctly if you have the time check out this page that really helped me: https://about-france.com/french/interrogative-2.htm