An Analogy: Post
Continuing with our post analogy, you can think of an end-system like a large apartment complex. Each apartment in the complex is an application.
The mailing address of the complex is like the IP address of the end-system. All running applications share it, just like all apartments share the street address. Each application running on a host has a different port number, just like each apartment has a different apartment number.
I don’t understand about “All running applications share it, just like all apartments share the street address.”. What is “application running”? And what are the things it shares?