A port is like an inlet or outlet from a computer connected to a computer network, formerly known as "Host". A PC has got more than 65 thousand ports. Even your favorite smart phones be it iPhone or Android sports ports for connecting with the outer world.
Our most beloved browsers connect to the websites using http protocol through port 80. It's a standard port and it belongs to an ancient fraternity of ports known as "System Ports". No ordinary program shall use a port belonging to system ports, as long as it's not a renegade working against the system.
The apartments build example shown in this video was conceived by yours truly. I hope watching the video will give you a better understanding of how ports are used in a TCP/IP based client/server distributed system.
Please note that the video is coming from my course titled "TCP/IP Socket Programming in C# .Net For Coders & Students". You may redeem the coupon code HALF in order to get a 50% discount. So, what are you waiting for, go join the course!!!