的 = 白 (white) + 勺. Its original meaning was 'bright' or 'a target/bullseye' (read dì, as in 目的 'aim'). But it was borrowed for the toneless particle 'de' — and in that role it became the single most common character in all of written Chinese.
的 is the #1 most frequent character in Chinese — it appears in roughly one out of every twenty written characters. It marks possession and description, like English 's or 'of': 我的 (my / mine), 你的 (your), 好的 (good one / OK). Put 的 between a describer and a noun: 我的书 (my book), 好看的字 (good-looking characters). Master this tiny word and your Chinese instantly sounds connected.
The little hook that ties things together — X 的 Y means 'X's Y'. The most common character of all.
的 is the most frequently used character in modern Chinese, full stop. About 4% of all written characters are 的. If you learn one particle, learn this one.