Hi August,
What is important to know is that the sound of the ç is the same of "s".
Thus the verb "conhecer", the sound of the sylab CE is is equal to SE, than if you write CO, the sound is like (KO). This is the reason to spell ÇO.
Resume, take care with the sound ÇA CE CI ÇO ÇU (sounds like SA SE SI SO SU).