Why are no .header and .cpp files added by the designer for the second window?
I try to code a tool with 3-4 windows.
As I added the 2. Form I realised that there was no .h file in header files folder and no .cpp file in source files for this 2. form.
Do I need to generate them on my own or what else do I need to do?
Adding a .ui file does not generate any class for it (the .h and .cpp files) automatically (because that might not be what you want in some cases).
To do that use a wizard: Add new -> Qt -> Qt Designer Form Class. This will generate a .ui, .h and a .cpp file for you.