In IS page, under Security ports, we will create the respective port and their alias.
Suppose, if we want make a call to client server using pub.client.http, we pass the url, method, authentication details parameters, etc… We do not have any option to pass port alias.
Than why do we create them?
Where exactly are we using this alias?
Sorry, but you must read IS Administration guide first to get the basics right.
Think about what happened when you disable a port, you have to pass something unique to service, right?
I agreee with Senthil that reading the IS Administrators Guide is essential in this case.
I will try to sort out somethings anyway:
Ports defined under Security → Ports in IS Admin are local ports on the IS used for incoming internal and external acces to this IS
The Alias is nothing but an indentifier for the port used by other parts of the configuration, i.e. Settings → QuiescePort.
When it comes to outgoing access you might want to look at Settings → URL Aliases, which can be assigned to the pub.client:http service. In this case define the same URL Alias name on any envioronment (DEV, QA, Production) with correct values for each environment where the service will be deployed to. By doing so you will not have to bother with how the pub.client:http will be provided with the details where to connect to as this is all defined in the URL Alias.
See IS Built-In-Services Reference for details on pub.client:http.