Cosa ne pensi ==> what do you think about it
what is the action/verb?
(tu) pensi = (you) think
who does the action?
(tu) = you, subject
what/who does the subject action (what do you think) ?
cosa = what, direct object. it is not the word cosa it self that is the direct object, but the element that the word cosa covers/refers to. I hope you follow.
to/of whom/what does the subject action the direct object (of whom/what do you think what)
ne = about it/of them, indirect pronoun
what about it/of them do you think? ==> what do you think about it/of them
I struggled with this this... I was convinced that 'ne' has a meaning amongst others of 'of them'..Question ...How many apples do you want...Answer In English..I want three. ..Answer in Italian ..I want three (of them).. NE voglio tre. In this type of question it usually means 'of them'..BUT ..NE can also mean 'Of it'. I looked at many example translations and it seems to default to 'of it( about it) unless it is apparently plural. Cosa ne pensi...What do you think of it (about it). Cosa ne pensi di loro or Cosa pensi di loro..What do you think of them.
We also have "ne" in French. They are two ways for using it. The easy one is for an undefined quantity. For example, talking about milk, "do you want some" is exactly "ne vuoi". Here you are talking about an abstract thing undefined, to think reffers to this thing then you have "che ne pensi" for "what do you think" in english.
Collins Italian grammar & practice makes a big point about how pensare, when meaning to think about something, goes with proposition "a" (pensare a), and that as such the corresponding pronoun should be CI, not NE.
Unless, of course, "pensare di" is also accepted. That would call for NE as the correct pronoun. Can anyone confirm?
I second you and Collins from the bottom of my analytic heart. In my german dictionary (leo.org) there is, apart from "pensare di fare qc" only "pensare a qc" but no "pensare di qc", so, according to what we've learned from Duolingo, it should be "ci pensi" and not "ne pensi". On the other hand, a quick internet research shows that the italians employ "cosa ne pensi". So I think about it as one of these typical rather nonsensical idioms.
CLOSE TO BOTTOM LINE: It seems like a very common phrase, so just MEMORIZE IT
PS: "Ci pensi" seems to be used however: Se ci pensi per un secondo. = If you think about it for a second. Or here, with another meaning: https://forum.wordreference.com/threads/ci-pensi-tu.35875/
I guess you got confused with Spanish... "Creo" in italian means "I create", not "I believe". Maybe you were talking about "credo" :)
"Cosa ne credi?" is actually wrong.
As a rule of thumb, you can / must use "ne" if it may replace "di [lui / lei / esso]".
"Cosa ne pensi?" means "Cosa pensi di [lui / lei / esso]?"
It is hard to tell, because sometimes italian "di" translates "of", other times "about".
In fact, "Cosa credi di lui?" is wrong. There are no rules about that, you have to learn it case by case.
Some verbs need / allow certain prepositions, some verbs not. Just like in english.