yes, the relationships shown in the diagram apply to the eCommerce database.
no, this does not mean that the manage relational table behavior is not needed, the manage relational table behavior is used to insert data to the relational tables to store related data.
yes, it is suitable to createating a eCommerce catalog with products that that have size and color options.
there are no detailed instructions available for getting started with this.
you would need to use data assist to create pages to mange the optiongroups table to create the Size and Color options groups.
then create pages to manage the options table, these pages will allow to add options like small, medium and large to the size options group and red, blue yellow to the color option group.
you would then use data assist to create pages to manage the products table to insert products.
you would need to use the manage relational table behavior here to assign options to the products using the productoptions relational table