What is a widget? A Widget is a generic term for a bit of self-contained code that displays a program, or a piece of a program. The Widgets are grouped by similarity. Simply click on the group tab to see the widgets within.
When you have the group selected and you see the list of widgets you can mouse over the widget to see a preview of what the widget would look like by clicking on the Magnifying Glass icon.
If you have previewed the widget and you like what you see then simply left click and drag the widget from the left and drop it within the layout on the right side. Depending on where you drop the widget it will resize.
When you are satisfied with the widget content and placement, click on the orange Publish button at the top right.