How to show the total number of items in customer shopping carts?
One way to do that is with a number badge placed on or next to the on the cart/shopping bag icon showing the number of items in the cart.
What is shopping cart module?
A cart module shows the items that have been added to the cart before the customer proceeds to checkout. The module also shows an order summary and lets the customer apply or remove promotional codes. The cart module supports signed-in checkout and guest checkout. It also supports a Back to shopping link.