Several parts combine into one character.

The etymology of 今 is debated — most likely it pictured a closed-mouth profile or a stoppered jar, both expressing "the moment of stopping / containment". From there, the meaning shifted to "now / this present moment" — time held still. Identical across 繁體 / 新字体 / 简体. Pairs with 古 (old / past, earlier batch) — 古今 (old + now) is the classical CJK term for "across all times".

Mandarin: jīn, level 1st tone. 今 is the everyday word for "now / this": 今天 (jīntiān, today), 今年 (jīnnián, this year), 今晚 (jīnwǎn, tonight), 今后 (jīnhòu, hereafter), 至今 (zhìjīn, until now), 古今 (gǔjīn, past and present). The temporal frame "今X" appears constantly: 今早 (this morning), 今下午 (this afternoon).

Japanese: TWO on-readings + irregular kun. コン (kon) is dominant in compounds — 今度 (kondo, this time / next time), 今週 (konshū, this week), 今月 (kongetsu, this month), 今晩 (konban, tonight), 今夜 (kon'ya, tonight). キン (kin) is rarer. The kun-reading いま (ima) is the everyday word for "now" — 今 (ima, now), 今すぐ (ima sugu, right now), 今に (ima ni, soon).

Critical irregular reading: 今日 (today) reads きょう (kyō), NOT こんにち (konnichi) in everyday speech. This is one of the foundational Japanese irregular readings every learner masters: 今日 → kyō. Compare 今週 (konshū) and 今朝 (kesa, this morning — another irregular). However, the formal greeting こんにちは (Konnichi wa, "hello") DOES come from 今日, with the older reading. 今日 has both readings depending on context — kyō for "today", konnichi for "the present day / nowadays" in formal contexts.

Memory aid: a stopper / closed lid — the present moment held still in time.