In order to understand what microservices are, first, we have to talk about monolith systems and their drawbacks. One-click buy cares about credit card numbers, and user info, while shipping cares about product attributes, like weight and height, and addresses.
Imagine you have Product, Order, Discount, and Payment in the same project.
So you call the Discount class from Order, and you pass the products.
Soon, when we actually get to the point of microservices we will talk about cohesion at the level of product or services.