It is used with events in wxPython. If you have a button lets say that when you press it pops up a dialog box. But there is also something else going on and you want the method that makes that dialog box to be called After the event function is done.
Woops, should have called them paramaters. If you have any that are needed then you put them as the second paramater but if there are no paramaters needed for the MeWin method then you dont need to have a second paramater.
Note that you dont put parentheses after the self.MeWin the the wx.CallAfter.