How are dictionaries of ideograms sorted?
Wikipedia


The second system of dictionary organization is by recurring graphic
components or radicals. (...) As most
Chinese characters are semantic-phonetic ones (形聲字), the radical
method is usually effective, thus it continues to be widely used in
the present day. However, sometimes the radical of a character is not
obvious. To compensate this, a &quot;Chart of Characters that Are Difficult
to Look up&quot; (難檢字表), arranged by the number of strokes of the
characters, is usually provided.

Here is what a chart of radicals in a dictionary looks like


You can otherwise search a character by its pinyin if you know it.

See also: https://www.quora.com/How-do-you-look-up-Chinese-characters-in-a-Chinese-dictionary