Logical aggregates: Characters that combine the meanings of one or more pictographs or ideographs to form a new meaning.
Ideographs: Characters that are comprised of abstract pictographic symbols and convey abstract meaning (e.g. directions, positional concepts, numeral concepts, etc); this type of characters are the basic units for forming the Chinese script.
Pictographs: Characters that use drawing to picture real-life concrete objects (e.g. animal, person, etc); this type of characters are also the basic units for forming the Chinese script.
Radicals: Tell something about the meaning of the character; they are also used to look up characters in a Chinese dictionary. To find a character you look for the radical in a radical list.

Semantic-phonetic compounds: Characters that consist of two parts: a semantic component indicating the meaning and a phonetic component indicating the sound.