Well , can anyone list some book Ishould read?

[ChrisW67]

Everybody should read some Shakespeare (or your language's great author) ... but I digress

I'd recommend the Blanchette/Summerfield book C++ GUI Programming with Qt 4 (2nd Edition)
There will be some slight differences if you use Qt5, but the principles remain valid.

[Zlatomir]

I also like to recommend Foundations of Qt Development (Johan Thelin) and also mention that the first edition of C++ GUI Programming with Qt 4 is available as free download.
Don't forget to also use the documentation, pretty much after you understood the concepts like: parent-child relationship, layouts, implicit sharing, signals and slots (a good overview can be found by following links in this page), you can use the documentation to look for classes that are added to Qt in newer versions (the books about Qt are a little old) and also different way to use some classes, one example: QThread recommended use is presented in the documentation and in books you might see classes derived from QThread.