because c followed by an a or o would make a hard c, it has to be changed to a cedilla (ç) to keep soft key.

Ex:

lancer ( to throw)

je lance

tu lances

il/elle/on lance

nous lançons

vous lancez

ils/elles/lancent

because an a or o would make "g" hard, an e has to be added after the g in order to keep the g soft.

Ex:

manger (to eat)

je mange

tu manges

il/elle/on mange

nous mangeons

vous mangez

ils/elles mangent