Same character, two readings. Toneless le is the grammar particle (completion, change of state). Third-tone liǎo is a verb meaning 'finish' or 'understand,' and it is also the 了 bound in V+得+了 / V+不+了 potential patterns — 受不了, 忘不了, 来得了 are all liǎo, never le.
memory
Two faces of 了: the toneless le is fast and weightless, a sigh at sentence-end; the third-tone liǎo is heavier, often paired with a verb of completion (了结, 了断) or comprehension (了解, 一目了然). If you can replace it with 'finish' or 'figure out,' it's liǎo.
Top hook is the position-variant of the 乙 Kangxi radical; here it is purely a visual indexing mark. Strict etymology reads 了 as a swaddled child whose limbs are bound, but the modern silhouette uses this single curved stroke as its radical home.
The downward hook closes the shape and historically traces the bound-baby's wrapped legs. As a learning component it functions as a pure positional stroke pinning the radical to the bottom of the square; it carries no independent meaning of its own.
