In Spain (Europe) a "Z" is always pronounced "TH" and a "C" before "E" or "I" is also pronounced TH:
Zaragoza [Tharagotha], Zamora [Thamora], Galicia [Galithia], Cáceres [Ka-theres]...
In some parts of Spain (Europe) and in all South-America "Z" with any vowel and "C" before E or I are pronounced like S (double SS).
Venezuela [Venesuela], Cáceres [Ká-seres]. Zaragoza [Saragosa]...
"C" before "A", "O" or "U" is always pronounced like "K" in any spanish dialect. Caracas [Karakas], Colombia [Kolombia], Cuba [Kuba], Costa Rica [Kosta-Rika], Puerto Rico [Puerto-Riko], ...
Spanish (español) or Castilian (castellano) is an Indo-European, Romance language that originated in northern Spain, and gradually spread in the Kingdom of Castile and evolved into the principal language of government and trade. It was taken to Africa, the Americas, and Asia Pacific with the expansion of the Spanish Empire between the fifteenth and nineteenth centuries.
Today, between 322 and 400 million people speak Spanish as a native language,making it the world's second or third most-spoken language by native speakers, depending on the sources
There are important variations among the regions of Spain and throughout Spanish-speaking America. In countries in Hispanophone America, it is preferable to use the word castellano to distinguish their version of the language from that of Spain, thus asserting their autonomy and national identity. In Spain, the Castilian dialect's pronunciation is commonly regarded as the national standard, although a use of slightly different pronouns called laísmo of this dialect is deprecated. More accurately, for nearly everyone in Spain, "standard Spanish" means, "pronouncing everything exactly as it is written," an ideal which does not correspond to any real dialect, though the northern dialects are the closest to it. In practice, the standard way of speaking Spanish in the media is "written Spanish" for formal speech, "Madrid dialect" (one of the transitional variants between Castilian and Andalusian) for informal speech.