Programmatically, you can check AddToCartController, where adding the product to cart functionality is written.
Also, if you drill down the method, you will see that different strategy classes are hit, based on which cart is recalculated.
you need to go to the controller which will lead you to further files methods which will include cart rules and model creation and association. You need to debug the whole flow to understand the full flow. While doing the debugging the OOB process you can understand where you can do the customizations as well.
You must be a registered user to add a comment. If you've already registered, sign in. Otherwise, register and sign in.