Firstly enable the assembly items, Matrix items features to use matrix assemblies. After enable the features in item records contain a matrix assemblies.
Matrix Assemblies: It is useful to planning the assembly items and production tracking purpose. Using the matrix to allows faster order entry items with different attributes, such as clothing items that come in different sizes and colors. Each group of attributes is unique and will have its own SKU, as well as its own price. Matrix items can be created at once by creating the parent item, selecting the options and system create the subitems. For example, a T-shirt could be defined by size and color.