Hi and welcome to devnet,
Are you also new to coding ? If so, then don't start with threads, that's a pretty complex subject that you should take on later after getting the basics correctly.
Also, for what you described there's no need for threads. Qt's asynchronous nature already provide what's needed.
Start with Qt's documentation. It also contains the Threading Basics
On a side note, it's Qt, QT stands for Apple QuickTime which you might also be interested in.