The pronunciation, meaning, form and etymology of a Chinese 'word' can be neatly packed inside a single kanji/Chinese character. (There is no equivalent in the English language to this.)
This is done by commingling small, interchangeable components known as 'radicals' (部首). These radicals are the fundamental building blocks of kanji. There are only 214 of them.
The tens of thousands of kanji out there (including those that are obsolete, forgotten or foreign to Japan) are built from these 214 radicals.
Radicals take positions: generally, they can appear above or below another radical, to the left or to the right of another radical, or can 'encase' another radical/kanji.
Radicals occasionally 'mutate' in appearance to fit certain positions.
Some radicals appear more frequently than others.