The Window

When creating a WPF application, the first thing you will meet is the Window class. It serves as the root of a window and provides you with the standard border, title bar and maximize, minimize and close buttons. A WPF window is a combination of a XAML (.xaml) file, where the <Window> element is the root, and a CodeBehind (.cs) file. If you're using Visual Studio (Express) and you create a new WPF application, it will create a default window for you, which will look something like this:

<Window x:Class="WpfApplication1.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="300" Width="300">
    <Grid>

    </Grid>
</Window>

The x:class attribute tells the XAML file which class to use, in 
this case Window1, which Visual Studio has created for us as well. You 
will find it in the project tree in VS, as a child node of the XAML 
file. By default, it looks something like this: 

using System;
using System.Windows;
using System.Windows.Controls;
//…more using statements
namespace WpfApplication1
{
    /// <summary>
    /// Interaction logic for Window1.xaml
    /// </summary>
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();
        }
    }
}

As you can see, the Window1 class is definied as partial, because it's being combined with your XAML file in runtime to give you the full window. This is actually what the call to InitializeComponent() does, which is why it's required to get a full functioning window up and running.
If we go back to the XAML file, you will notice a couple of other interesting attributes on the Window element, like Title, which defines the title of the window (shown in the title bar) as well as the starting width and height. There are also a couple of namespace definitions, 

Important Window properties

The WPF Window class has a bunch of interesting attributes that you may set to control the look and behavior of your application window. Here's a short list of the most interesting ones:
Icon - Allows you to define the icon of the window, which is usually shown in the upper right corner, right before the window title.
ResizeMode - This controls whether and how the end-user can resize your window. The default is CanResize, which allows the user to resize the window like any other window, either by using the maximize/minimize buttons or by dragging one of the edges. CanMinimize will allow the user to minimize the window, but not to maximize it or drag it bigger or smaller. NoResize is the strictest one, where the maximize and minimize buttons are removed and the window can't be dragged bigger or smaller.
ShowInTaskbar - The default is true, but if you set it to false, your window won't be represented in the Windows taskbar. Useful for non-primary windows or for applications that should minimize to the tray.
SizeToContent - Decide if the Window should resize itself to automatically fit its content. The default is Manual, which means that the window doesn't automatically resize. Other options are Width, Height and WidthAndHeight, and each of them will automatically adjust the window size horizontally, vertically or both.
Topmost - The default is false, but if set to true, your Window will stay on top of other windows unless minimized. Only useful for special situations.
WindowStartupLocation - Controls the initial position of your window. The default is Manual, which means that the window will be initially positioned according to the Top and Left properties of your window. Other options are CenterOwner, which will position the window in the center of it's owner window, and CenterScreen, which will position the window in the center of the screen.
WindowState - Controls the initial window state. It can be either Normal, Maximized or Minimized. The default is Normal, which is what you should use unless you want your window to start either maximized or minimized.
There are lots of other attributes though, so have a look for yourself and then move on to the next chapter.