gui application for serial port communication

[Lykurg]

what isn't this forum for helping qt user

Yes of course, but only if both sides are willing. Helping does not mean to do the work for you and present you the result. If we should help, then we expect that you also are willing to do your part. And as I can see, your problem is not about serial port, it is about basic understanding using a library. Have you read the documentation about how to use dynamic libraries? (See the qmake documentation and LIBS as a starting point.)