how do you know when a c makes a "c" sound like in english and when it make a "s" sound??
I need help
If I remember correctly, the "c" can take two different sounds in English. If it sounds like a "k" it is referred to as being hard. If it sounds like an "s" it is referred to as being soft.
In Spanish, if a "c" is followed by either an "e" or an "i" it is soft. Followed by any other letter (or in the rare case that it's the last letter in a word) it is hard.
Also, in Spanish the "s" and the soft "c" are never buzzed, as the English "z". Spanish speakers have a hard time differentiating between "president" and "precedent".
Oops! I forgot about "y". It does the same thing to the "c" that the "i" does.
By the way, the same rules generally apply in English.
I couldn't put it any better than CalvoViejo!
You may also find these references from here at SpanishDict useful:
Spanish alphabet - how do letters sound
I hope that helps!