There's a lot of differences.

Z sound how said C95, is a /θ/. And always sound like /θ/

Ej: Zapatilla.

With C there are two sounds. We can find a /θ/ sound only if the next letter is an "e" or and "i"

ej: cielo, cereza, in these words "c" sounds like "z"

If the next letter is "a", "o", "u"; c sounds like /K/. 

ej: Casa, coco, cuchara. C before these letter NEVER sounds like /θ/

The 'th' sound - I'm talking about /θ/ - only comes with a "z" or with a "c" before an i or an e. So words like 'zapato, 'cielo' or 'cerveza' would sound 'thapato', 'thielo' and 'thervetha'. Only "s" is pronouced like /s/.

However, Spain has many dialects and not all them follow this pattern :) This is to be considerated standard Peninsular Spanish or "Castillian Spanish". Hope this helps!

Yes, our pronunciation is different, and not easy to foreigners, I think.

The sounds can be grouped in that way:

sa se si so su (no problem here)

ca que qui co cu (can be read as ka ke ki ko ku. Ce and ci make a differen sound!)

za ce/ze ci/zi zo zu (And here they are. We usually wrote incorrectly the words with ce/ze or ci/zi, as the sound is the same.)

Please, use this link to hear the pronunciation of people of different countries.

http://forvo.com/word/cereza/#es

SHILA, first you are a beautiful girl.

regarding your second question, All people in all latin america, I speak billions people. Pronunce the z and c like s sound. in fact, the most people here think that people in spain sounds funny. but everything is in the eye of where you look. spanish speakers understeand with two sound without problem

Thank for your answers, my friends.

So now I have a question: if I pronounce z and c like s sound, don't I seem like a fool stranger??I mean will I be coprehensible enough just like a native Spanish speaker?isn't it funny or ridiculous for native speakers??

I really care about normal speaking.