DDD Ports and Adapters with Onion architecture, what goes where?

trying to figure out some concepts and haven't been able to understand

What is a use-case in the Ports and Adapters architecture ?

What an implementation of a use-case would look like ?

What is a use-case concern ?

Where does it fit in the Infrastructure or Domain, it says it goes in the Application, well there is the Application Core and the Application Service which from my understanding are different ?

On the left side, the adapter depends on the port and gets injected a concrete implementation of the port, which contains the use case. On this side, both the port and its concrete implementation (the use case) belong inside the application; On the right side, the adapter is the concrete implementation of the port and is injected in our business logic although our business logic only knows about the interface. On this side, the port belongs inside the application, but its concrete implementation belongs outside and it wraps around some external tool.

https://herbertograca.com/2017/09/14/ports-adapters-architecture/#what-is-a-port