1. the practical, essential aspects of something
understand the nuts and bolts of the business
The 'nuts and bolts' of something are the internal or essential parts of something that make it work. In a figurative sense, when we focus on the 'nuts and bolts' of something, we move beyond the superficial or unnecessary stuff and focus on the fundamental, practical elements. This is mainly used in business contexts, relating to production or just to business operations in general.