Associative compounds
The principle of forming characters by drawing pictures is easy to understand, but pictographs cannot express abstract ideas. So the ancients invented the "associative compounds," i. e., characters formed by combining two or more elements, each with a meaning of its own, to express new ideas. Thus, the sun and the moon written together became the character (ming), which means "bright"; the sun placed over a line representing the horizon formed the ideogram (dan) which means "sunrise" or "morning".
Pictophonetics
Though pictographs and associative compounds indicate the meanings of characters by their forms, yet neither of the two categories gives any hint as to pronunciation. The pictophonetic method was developed to create new characters by combining one element indicating meaning and the other sound. For instance, 爸 (ba) the Chinese character for "papa" is formed by the element 巴 (ba) which represents the sound and the element 父 (fu) which represents the meaning (father). Likewise the character 芭 (ba) is formed by 巴 (the sound) and ++, indicating a plant. In this way, more and more characters were made until such pictophonetics constitute today about 90 percent of all Chinese characters.