A widget is a module that lets you add specific features to pre-defined sections of your website. The location of those sections varies a bit depending on which theme your site is using but generally they are in the footer of your site and where you see your group's description.
Your site comes with a few widgets you can use:
Button Widget - create a custom button for an important link
Contact Info - show visitors how to get ahold of you
Group Description - show your groups description and social links
Links - display important links
Sponsors - feature images and links from your Advertising section
YouTube Video - simply add a link to YouTube to embed a video
Text - add any text or HTML to your site
When you go to the Widgets subpage within your site's Appearance menu, you'll see them listed out along with the various parts of your site where they can be included.
This example site is using the Springfield theme which contains four widget sections: Sidebar, Bottom-Left, Bottom-Middle and Bottom-Right. Each theme is a little different, but most will have at least three sections in the footer and one or two other areas for widgets.
By default, your widget sections will contain a Group Description, Links and Contact Info. Customizing your widgets is usually jut a matter for dragging and dropping things on the screen (similar to how you manage your site's navigation menu).
Important Note
When you change the theme of your site, you will need to re-add your widgets where you would like them to appear. Because each theme has different locations where widgets appear, your old theme cant tell the new one where to put the widgets, so it moves them into the "Inactive Widgets" section you see on the admin page above. After you change the theme, simply drag your widgets to the locations where you'd like them to appear in the new theme and you are all set
Removing Widgets
To remove a widget, just click the widget's name and click "Delete." Or if you might want to save the settings from that widget for future use, just drag it over to the left into the "Inactive Widgets" section. Like this:
Adding Widgets
You can have as many of each widget as you like - if you want to feature 5 YouTube videos in one area, just add 5 YouTube widgets to one section. OR if you want to add a few different HTML elements like a Twitter timeline and Facebook Fan Page Box, just add 2 Text widgets. To add a new widget, drag the type of widget you would like from the list on the left, drop it in the section you'd like it to appear and click the Save button on the widget.
Arranging Widgets
Once you've added widgets, you can arrange them within a section by simply dragging them to the position where you would like them to appear.