Well libraries are simply not interchangable. Each library does hold a couple of objects defining typically the functionality given in the general naming.
Some namings may have changed between Qt4 and Qt5, but not network to anything.
Also when your application is requiring network functionality, but is missing it in the link process, you should see somewhere error messages.
I would suggest that it is best when you are checking out examples from the tutorials. There are the network examples and there is the testlib functionality
however, Qt offers more different aspects and it may make sense for you to check out those as well.