Generally, when you know the shape of a character, but do not know the pronunciation or meaning of the character, you can use the radicals of the character to look it up.

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Chinese characters are all square characters, and the radicals are the components that make up a compound character. In ancient times, people called the left part of the left and right parts of a compound character "radical", and the right part "phonetic". In modern times, in order to reduce the difficulty of recognizing the characters, we call all parts of the compound character "radical".