основа(the) nuts and bolts: the basic, practical details of a job or other activity. Law school teaches wonderful theory but it doesn't teach the nuts and bolts of actually practising law. often + of). CI Alexander Demidov)
практическая сторона(the practical facts about a particular thing, rather than theories or ideas about it: " When it came to the nuts and bolts of running a business, he was clearly unable to cope. CALD Alexander Demidov)