Once you have filled your widget area with your desired widgets, you will still need to tell the theme on which posts you would like to display this widget area. To do this see the following:
To Insert The Widget Area as a Sidebar:
On each post creation page you will see on the right hand side below the "tags" box, an additional content boxes entitled Sidebar.
This boxes allow you to select which widget area is to be used specifically on that post for the sidebar. This may be different for each and every post.
To Insert The Widget Area as a footer:
The widgets page already contains a "Footer" widget area. This is the footer widget area and widgets added in here will appear in the theme's footer. The footer accepts 4 widgets or less.