Where the shape comes from
A hand gripping a brush, the bristles at the base and the fingers closed around the shaft above. Add a bamboo shaft on top and it becomes 笔, a writing brush, a pen; drawn making lines around the boundary of a field, it gives 画, to draw, a painting; and it sits, worn down to a single stroke, inside 书, a book, to write.
汉字 filed under 聿
No published character on HSK Guide is filed under this radical yet. 汉字库.