What is the primary purpose of a nail file?

The primary purpose of a nail file is to shape and smooth nails. Nail files are essential tools in a nail technician's kit, designed specifically to achieve a desired nail shape by refining the edges and creating a smooth finish. When using a nail file, a technician can effectively shorten, lengthen, or round the edges of the nails, allowing clients to have beautifully shaped nails that suit their preferences and style. This is a fundamental skill in nail care, as a well-shaped nail not only looks aesthetically pleasing but also prepares the nail for other services, such as polishing or applying nail enhancements.

The other options refer to different aspects of nail care but do not embody the primary function of a nail file. For example, decorating nails involves fashioning art or designs, polishing is about applying a shiny finish, and cleaning under the nails pertains to hygiene, none of which are the primary uses for a nail file itself.