Several parts combine into one character.

Compound ideograph: 聿 (a hand holding a brush) on top + 曰 (mouth speaking) below. The encoded scene: a brush capturing speech in writing. The character itself describes the act of becoming a written record.

Three forms diverge sharply: 繁體 書 / 新字体 書 / 简体 书. Mainland simplified Chinese reduced 书 to a few abstract strokes — one of the most extreme simplifications in the script. The traditional and Japanese form 書 still preserves the brush-and-mouth picture; the simplified 书 has left almost no trace of either component.

書 covers writing, books, calligraphy, and documentation. Calligraphy itself is 書道 (shodō, "the way of writing") in Japanese, 書法 (shūfǎ) in Chinese — both rooted in this character.

Mandarin: shū, level 1st tone. 书 (shū, book), 书本 (shūběn, books), 书包 (shūbāo, schoolbag), 看书 (kàn shū, to read books — common verb-object pair), 读书 (dúshū, to study / read), 教科书 (jiàokēshū, textbook), 图书馆 (túshūguǎn, library). The everyday verb for "to write" in Mandarin is 写 (xiě), with 书 reserved for nouns and certain literary verbs (书写 shūxiě, to write formally).

Japanese: on-reading ショ (sho) for compounds — 読書 (dokusho, reading), 図書館 (toshokan, library — note slightly irregular reading), 辞書 (jisho, dictionary), 文書 (bunsho, document), 書類 (shorui, paperwork), 書道 (shodō, calligraphy), 教科書 (kyōkasho, textbook). Kun-reading か.く (ka.ku, to write) is the everyday verb. 書く is the central writing verb; 描く (also kaku, "to draw") is its sibling for drawing.

Memory aid: a brush above a mouth — speech captured in ink. (In simplified, just remember "abstract scribbles" = book.)