i want to make a simple database for online shopping  however i am confused about certain points
i know i need to have a customer entity , product entity and order item entity.
According to my understanding many customers can order many products and when the same customer orders later on he needs to be assigned a new order id  along with the product id  so that calls for a composite key but what i specifically lack in is defining relationships and cardinality.

can some one please help me structuring the design for the shopping cart .

thanks in advance