Add a qDebug () in your get_started_info() slot to check if it is getting called when the triggered signal is fired. Try to create a QMessageBox to see if it will show.
Qt Code: 
  1. QMessageBox::information(this,"title","message");// dont forget to include QMessageBox
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You can go to the UI file in the designer and go to the action editor and right click your action , go to slot and press on triggered ( it will then automatically create a slot for you in your mainwindow ) and inside it create your dialog.
Did you create a class memember from your dialog ?
Qt Code: 
  1. get_started *one; //in your mainwindow under private
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Good Luck.