When I have added a comboBox to the WPF window, how do I add items to the comboBox? Int the XAML code for the design or in NameOfWindow.xaml.cs file?
You can fill it from XAML or from .cs. There are few ways to fill controls with data. It would be best for You to read more about WPF technology, it allows to do many things in many ways, depending on Your needs. It's more important to choose method based on Your project needs. You can start here. It's an easy article about creating combobox, and filling it with some data.