Firstly there is a thing named as IP Address which means that which computer on
a network to send the data coming from the other computer network.

Every Computer/device has a 16 bit port number. which means there are 65536 
ports present in a computer. 

0-48000 port numbers are booked already by system, some classical softwares 
like mongodb, express and more and some for some specific companies. 

Port Numbers after 48000 you can use.