。
Mother taught me how to make osechi.
Literal
Mother [subject-が] me [to-に] osechi [gen-の] making-way [obj-を] taught-for-me.
おせち (お節料理) is the elaborate New Year's food set — layered lacquered boxes of symbolic dishes, each representing a wish for the new year (kazunoko for fertility, black beans for health, etc.). Making it is a multi-day family affair, and being taught to make it is a cultural inheritance moment. 作り方 is the productive [verb stem]+方 ('way of X-ing,' 'how to X') noun pattern.