Several parts combine into one character.

Compound character: 立 (variant of 辛, a sharp tool / pin) + 木 (tree) + 斤 (axe). The encoded scene: an axe just chopping a fresh tree. The ancient definition of "new": that which has just been cut, still bearing the scent and light of the fresh wood. Identical across 繁體 / 新字体 / 简体. Pairs with 古 (old, previous entry) as one of the fundamental temporal oppositions.

The etymology beautifully grounds an abstract adjective in a concrete sensory experience — the smell of just-cut wood. Modern speakers don't feel this anymore, but the character preserves it.

Mandarin: xīn, level 1st tone. 新 covers freshness, recency, and the new in opposition to the old: 新年 (xīnnián, New Year), 新闻 (xīnwén, news), 新鲜 (xīnxiān, fresh), 重新 (chóngxīn, again / anew), 创新 (chuàngxīn, innovate), 新郎 (xīnláng, groom — "new bridegroom"), 新娘 (xīnniáng, bride). 重新 and 创新 carry strong "starting over / making fresh" weight in modern usage.

Japanese: on-reading シン (shin) for compounds — 新聞 (shinbun, newspaper — Japan's oldest dailies date to the 1870s), 新年 (shin'nen, new year), 最新 (saishin, latest / newest), 革新 (kakushin, reform / innovation), 新幹線 (shinkansen, "new trunk line" = bullet train), 新宿 (Shinjuku, Tokyo's major district — "new lodging"). Kun-reading あたら.しい (atara.shii, new) is one of the highest-frequency Japanese adjectives. Fresh things use 新, modern food often pairs with 新鮮 (shinsen, fresh).

The word 新幹線 (Shinkansen) — Japan's legendary high-speed rail since 1964 — uses 新 to declare itself "the new line" — and the name has stuck for over half a century.

Memory aid: an axe just struck a tree — the scent of fresh-cut wood = newness.