The letters "G" and "C"
The letters "G" and "C" can represent either a stop consonant or a fricative. Specifically, "G" can represent both /g/ and /ʒ/ , while "C" can represent /k/ or /s/ . In order to know which phoneme to use, you must consider the next letter (accents don't matter here). If it is "O", "U" or "A", the consonant is a stop, for example:
goût [gu]
aigu [egy]
galon [galõ]
coupable [kupabl]
capable [kapabl]
vécu [veky]
If, however, the next letter is "E" or "I", then the fricative should be pronounced, e.g.:
geler [ʒəle]
givre [ʒivʁ]
cela [səla]
cire [siʁ]
This actually makes sense since /s/ and /ʒ/, which are pronounced in the front of the mouth, precede front vowels, while /k/ and /g/ precede non-front vowels. Note that if one is to pronounce "C" as /s/ before "O", "U" or "A", a cedilla is used, e.g.: façon, reçu, ça.