when you read these two consonants,"z" a little weak,it doesnt need strong breath of air;"c"is accompanied by a puff of exhaled air.

And z is like z in the word zero, C is like zw in the word of Zweig or in the German number Zwei

Z like: kids,words C like :cats students

Do you mean "zhi and chi? or " ze and ce? It is hard to explain here. but Zh is a little similar to J in English, Ch is similar to Ch in English. You may start from using the English pronunciation at first, then try to listen repeatedly to learn the real Chinese pronunciation.

"Z" is like the consonant in "zee" and "c" is like "ts" in "tsi"