Thank you OsiedleRuda and kioko.
I think the best way to hear the sound is to say two words where ć/ci are at the end, like: znać and śmieci. With ć you "cut" the sound, but with ci you make it longer by saying i at the end (Polish i)
The grammars say that ci, when not followed by a vowel, also has an "i" sound, as if it would be a (sorry for the spelling) "ći" - so there is that difference between znać and śmieci.
But what about ci followed by a vowel: is ciągle pronounced different from a (made-up and again wrongly spelled, sorry) "ćągle"?
I disagree with ż and rz sounding exactly the same, though - Żoliborz (a Warsaw district) combines both sounds, but the ż sounds more like it's made with the lips, whereas the rz sound is made more with the tongue.
Oh, isn't the rz in that place name pronounced sz (end of the word)?
but I'm sure a Wikipedia search would explain why.
The "problem" is that Wikipedia, as all grammars I have come across, say that ć/ci, ś/si, ź/zi, ż/rz, u/ó are all pairs of identical sounds...