Widgets are mini-applications that can be pinned to your home screen the same way you pin icons. More than just an application shortcut, widgets give you real-time information such as the latest news or your e-mail without the need to launch an application.
You can even interact with what is shown, scrolling through your inbox on the mail widget or changing track on the music widget.
To add a widget, open the applications drawer and open the tab Widgets. Long press on the widget that you want to move and drag it to the desired zone on the home page.
Once pinned, some widgets can be resized, to do so hold one of the blue dots that you will move in the desired direction. Change the size of the widget can also often change the amount of information displayed by the widget.
To move again the widget or remove it, follow the same procedure than for icons.