员 (traditional 員) set a round mouth 口 over a cauldron (later the money-shell 贝) — originally 'round', then 'a counted unit'. People counted for pay became personnel: heads on the roster.
员 staffs every workplace: 服务员 (waiter — the word you'll call out most in China: 服务员! 点菜!), 售货员 (shop clerk), 演员 (actor), 党员 (party member), 会员 (member — every app wants you to be one). The -员 suffix is Chinese's '-er/-ist' for staffed roles. Learn it once, read half the badges in any building.
A mouth 口 counted over money 贝 — a MEMBER of the staff.
服务员! shouted across a restaurant is perfectly polite in China — timidity keeps you hungry.