Manyogana (万葉仮名 man'yōgana) was the "alphabet" of Chinese characters (hanzi) used in Classical Japanese to write Japanese phonetically. That is, a Chinese character was used only to represent a sound, without making use of the semantic value. Manyogana became obsolete in modern Japan, being supplanted by the systems of katakana and hiragana which derived from it-- katakana characters consist of radicals or small components of manyogana, while hiragana are stylized cursive versions of the corresponding manyogana.
For example, the character 礼 became the katakana レ and the hiragana れ. One can easily see how this was done: For the katakana, the right half of the character was borrowed, while the hiragana is just the cursive style of the character.