0 used to ask or talk about a choice between two or more things -- quale, quali, che
1 used to show what thing is being talked about or written about -- il quale, che, il che
These are principles which we all believe in. Questi sono principi in cui noi tutti crediamo.
2 used to give more information about something -- il quale, che, il che
The book, which includes a map, gives you all the information you need about Venice. Il libro, con mappa acclusa, dà tutte le informazioni necessarie su Venezia.
3 used in questions etc when asking someone to point out, state etc one or more persons, things etc from a particular known group -- quale; chi
4 (used to refer to a thing or things mentioned previously to distinguish it or them from others; able to be replaced by that except after a preposition; able to be omitted except after a preposition or when the subject of a clause) (the) one(s) that -- che; il quale, la quale, i quali, le quali
5 used, after a comma, to introduce a further comment on something -- che; il che*; cui