what does cest ça mean?

It means: "What is this?" Literally: What is this that is this. "Qu'est ce que c'est" and "Qu'est ce que ça" are really not different in meaning at all. At least not that I could discern. -- Chris (not a native speaker).

It's actually "Qu'est-ce que c'est que ça ?"

You were missing another 'que' - yep, there are in fact three in this form of the question!

When spoken though, this is usually run into something much shorter that sounds far less cumbersome: kess-kuh-sek-sah?
There's not much point trying to understand the phrase word by word as it doesn't make much sense that way. It just means: What's that?

On it's own, "c'est ça" means "that's it". (but in the above, it would be '...it is that').

Hope that helps!

Bonjour Tina !

Actually "c'est" means "it is / that is / this is", whereas "ça" only means "it / that / this" :)

Here are our related lessons:
https://french.kwiziq.com/revision/grammar/cest-means-it-is

https://french.kwiziq.com/revision/grammar/ca-means-that-this-or-it-pronoun

Bonne journée !