Well understanding google ads its like a process and you cannot learning in just a few words Its like asking someone to teach you math in one day .You need to take the time to implement ,fail ,learn all time the new changes that take places etc Also its not just about the theory its also about practical things by implementing campaigns etc .This its the way to learn
I think you have a long way to go. It cannot be explained in 2 lines, I suggest you read Google sources in this field.