Yes, you can use a messagebox, or if you open the Toolbox (Ctrl + X) or View > Toolbox, you can drag a label to the GUI and then use labelname.Text = “My Message”;
Messageboxes suck for output – unless you like speaking through modal dialogs.
WPF and winforms are vastly different beasts. For winforms, I used to just build a multiline textbox and append lines to the bottom to catch the output sort of messages one would Console.WriteLine(). WPF wants you to do some databinding stuff I never quite got my head around enough to explain.