Several parts combine into one character.

Compound character: 亻 (person) + 吏 (an official / one who manages affairs). The encoded meaning: "to send someone on a task / to make someone do something" → "to use / to make use of / to dispatch". From the original sense of dispatching messengers grew the modern abstract sense of "using" anything. Identical across 繁體 / 新字体 / 简体.

Mandarin: shǐ, dipping 3rd tone. 使用 (shǐyòng, to use), 大使 (dàshǐ, ambassador — "great messenger"), 大使馆 (dàshǐguǎn, embassy), 使得 (shǐde, to cause / make), 即使 (jíshǐ, even if — important conjunction), 假使 (jiǎshǐ, supposing / if). 即使 is a key intermediate-level conjunction every Mandarin learner needs.

Japanese: on-reading シ (shi) — 使用 (shiyō, use / usage), 大使 (taishi, ambassador), 大使館 (taishikan, embassy), 使命 (shimei, mission / duty), 駆使 (kushi, to handle skillfully — used in business / linguistic contexts: 二か国語を駆使する = to handle two languages skillfully), 天使 (tenshi, angel — "heaven's messenger"). Kun-reading つか.う (tsuka.u, to use) is among the highest-frequency Japanese verbs — 使う covers any kind of usage: tools, time, money, language, energy.

Note the cross-CJK grammatical role: 使 also serves as a CAUSATIVE marker in classical and formal Chinese — 使我快樂 = "make me happy". In modern Mandarin this role has been mostly replaced by 让 (ràng), but 使 survives in formal writing.

The trio 使う(tsukau, use) / 使用(shiyō, usage) / 使い方(tsukaikata, way of using) is foundational for any Japanese instructional vocabulary.

Memory aid: a person directing another — making someone do, using someone for a task.