From Jonathan Gardner's Korean Notebook
In Chinese writing (한자), characters can be classified by a root or parent character. This is called the "radical".
- Example: The character 三 is the same as the character 一 with two additional lines added to it. Therefore, this is rather obviously derived from it. Or, in other words, the radical for 三 is 一.
There are only a few dozen very common radicals. The rest are relatively uncommon, and you'll learn them as you learn the characters that use them.
When looking up a character, you can look it up by sound or by the total number of strokes. Both of these can be unwieldy, particularly when you can easily identify the radical of the character. In a Chinese character dictionary, the characters are usually organized by radical, so you simply need to flip to that section, count up to the number of strokes, and find your character from among the two or three others that share the same radical and stroke count.