Hotel front desk, or the local police station if you rent. You can also register online yourself (English): s.nia.gov.cn/mps/main-en.html. See the bilingual note for your landlord.
住酒店找前台；租房去当地派出所。也可以自己在网上登记（英文页面）：s.nia.gov.cn/mps/main-en.html。给房东的双语说明见 host-registration.html。
Bring your passport. Major carriers (China Mobile / Unicom / Telecom) sell prepaid tourist SIMs at airport and city stores.
带上护照。中国移动 / 联通 / 电信在机场和市区门店都有预付费卡。
Both accept foreign cards (Visa / Mastercard) for many merchants; a Chinese bank account or e-CNY makes it smoother.
两者都支持绑定外卡（Visa / Mastercard）用于多数商户；有中国银行账户或用数字人民币更顺畅。
Google Maps is limited in mainland China; Baidu Maps / Amap work everywhere. A translation app with photo & voice input helps a lot.
谷歌地图在大陆受限；百度地图 / 高德地图可用。带拍照和语音输入的翻译应用很有用。
Police may ask to see it. Keep the original safe and carry a paper copy or a photo on your phone.
警察可能查验。原件放好，随身带复印件或手机里的照片。
These work from any phone in mainland China, free of charge.
大陆任何手机都可拨打，免费。
Your entry stamp shows the allowed stay. Overstaying can bring fines and future-visa problems — ask the local exit–entry office if in doubt.
入境章上有允许停留期限。逾期可能被罚款并影响以后签证——不确定时问当地出入境管理部门。