nuts and bolts --------- 基本细节，要点（非正式）

英文释义
(INFORMAL) The basic, sometimes mundane but essential aspects of any operation; practical facts about how something works, often used in contrast with theoretical knowledge. (NOTE:“nuts”in this usage refers to metal fasteners)

例句
In spite of having an MBA degree, when I first took over management of an actual company it took me many months to really understand the nuts and bolts of the business.
尽管拥有MBA学位，当我第一次担任一家实际企业的管理职务时，我还是花了好几个月时间才真正理解了商业的要点。