Features provide sections of your site that pertain to a specific kind of content, such as a blog, publication or announcement. You can enable, make private or disable features individually within the Control Panel.  In general, making an element "disabled" will cause all of the features content/elements to be removed from the site. Marking the element "private" will give only the administrators access to the content, and marking it "public" will give the public free access to view the content. Most features come with helper elements to assist with publishing and managing your content, including:

Menu Entry -  Most features will automatically create a link in your site's primary menu that will show all the content  of the feature. If you mark the feature Private only administrators will see the link to this feature. So, if you enable the Announcement feature, an "Announcement" link appear in your primary menu that will display all of your announcements.

Widget - Think of a widget as a block that contains web content of some sort. This "web content" could be a variety of things, from a list of featured posts, to a gallery of recent images, to a site search tool. The great thing about widgets is that you can choose where they appear within your site's layout. The Control Panel provides and easy way to arrange your widgets by dragging and dropping them to marked sections of your site's layout.

Features are can be enabled or disabled in the Control Panel. See Managing Features.